Screen related adaptation of higher order ambisonic (hoa) content

ABSTRACT

Systems and techniques for rendering audio data are generally disclosed. An example device for rendering a higher order ambition (HOA) audio signal includes a memory configured to store the HOA audio signal, and one or more processors coupled to the memory. The one or more processors are configured to perform a loudness compensation process as part of generating an effect matrix. The one or more processors are further configured to render the HOA audio signal based on the effect matrix.

This application claims the benefit of:

U.S. Provisional Application Number 62/241,709, filed 14 Oct. 2015;

U.S. Provisional Application Number 62/244,149, filed 20 Oct. 2015; and

U.S. Provisional Application Number 62/255,353, filed 13 Nov. 2015, theentire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to audio data and, more specifically, coding ofhigher-order ambition audio data.

BACKGROUND

A higher-order ambitions (HOA) signal (often represented by a pluralityof spherical harmonic coefficients (SCH) or other hierarchical elements)is a three-dimensional representation of a sound field. The HOA or SCHrepresentation may represent the sound field in a manner that isindependent of the local speaker geometry used to playback amulti-channel audio signal rendered from the SCH signal. The SCH signalmay also facilitate backwards compatibility as the SCH signal may berendered to well-known and highly adopted multi-channel formats, such asa 5.1 audio channel format or a 7.1 audio channel format. The SCHrepresentation may therefore enable a better representation of a soundfield that also accommodates backward compatibility.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating spherical harmonic basis functions ofvarious orders and sub-orders.

FIG. 2 is a diagram illustrating a system that may perform variousaspects of the techniques described in this disclosure.

FIG. 3 is a block diagram illustrating, in more detail, one example ofthe audio encoding device shown in the example of FIG. 2 that mayperform various aspects of the techniques described in this disclosure.

FIG. 4 is a block diagram illustrating the audio decoding device of FIG.2 in more detail.

FIG. 5 is a flowchart illustrating exemplary operation of an audioencoding device in performing various aspects of the vector-basedsynthesis techniques described in this disclosure.

FIG. 6 is a flowchart illustrating exemplary operation of an audiodecoding device in performing various aspects of the techniquesdescribed in this disclosure.

FIG. 7A shows an example mapping function that may be used to maporiginal azimuth angles to modified azimuth angles based on a referencescreen size and a viewing window size.

FIG. 7B shows an example mapping function that may be used to maporiginal elevation angles to modified elevation angles based on areference screen size and a viewing window size.

FIG. 8 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow for the first example.

FIGS. 9A and 9B show examples of computed HOA effect matrices.

FIG. 10 shows an example of how an effect matrix may be pre-rendered andapplied to the loudspeaker rendering matrix.

FIG. 11 shows an example of how if the effect matrix may result in ahigher order content (e.g., 6^(the) order), a rendering matrix in thisorder may be multiplied to pre-compute the final rendering matrix in theoriginal order (here 3r^(d) order).

FIG. 12A show an example mapping function that may be used to maporiginal azimuth angles to modified azimuth angles based on a referencescreen size and a viewing window size.

FIG. 12B show an examples mapping function that may be used to maporiginal elevation angles to modified elevation angles based on areference screen size and a viewing window size.

FIG. 12C shows a computed HOA effect matrix.

FIG. 13 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow.

FIG. 14A show an example mapping function that may be used to maporiginal azimuth angles to modified azimuth angles based on a referencescreen size and a viewing window size.

FIG. 14B show an examples mapping function that may be used to maporiginal elevation angles to modified elevation angles based on areference screen size and a viewing window size.

FIG. 14C shows a computed HOA effect matrix.

FIG. 15 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow.

FIG. 16A show an example mapping function that may be used to maporiginal azimuth angles to modified azimuth angles based on a referencescreen size and a viewing window size.

FIG. 16B show an examples mapping function that may be used to maporiginal elevation angles to modified elevation angles based on areference screen size and a viewing window size.

FIG. 16C shows a computed HOA effect matrix.

FIG. 17 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow.

FIG. 18A show an example mapping function that may be used to maporiginal azimuth angles to modified azimuth angles based on a referencescreen size and a viewing window size.

FIG. 18B show an examples mapping function that may be used to maporiginal elevation angles to modified elevation angles based on areference screen size and a viewing window size.

FIG. 18C shows a computed HOA effect matrix.

FIG. 19 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow.

FIGS. 20A-20F are block diagrams illustrating example implementations ofaudio rendering devices configured to implement the techniques of thisdisclosure.

FIG. 21 is a flowchart illustrating an example process that a system mayperform to implement one or more techniques of this disclosure.

FIG. 22 is a flowchart illustrating an example process that a system mayperform to implement one or more techniques of this disclosure.

FIG. 23 is a flowchart illustrating an example process that a system mayperform to implement one or more techniques of this disclosure.

DETAILED DESCRIPTION

The evolution of surround sound has made available many output formatsfor entertainment nowadays. Examples of such consumer surround soundformats are mostly ‘channel’ based in that they implicitly specify feedsto loudspeakers in certain geometrical coordinates. The consumersurround sound formats include the popular 5.1 format (which includesthe following six channels: front left (FL), front right (FR), center orfront center, back left or surround left, back right or surround right,and low frequency effects (LFE)), the growing 7.1 format, variousformats that includes height speakers such as the 7.1.4 format and the22.2 format (e.g., for use with the Ultra High Definition Televisionstandard). Non-consumer formats can span any number of speakers (insymmetric and non-symmetric geometries) often termed ‘surround arrays’.One example of such an array includes 32 loudspeakers positioned oncoordinates on the corners of a truncated icosahedron.

The input to a future MPEG encoder is optionally one of three possibleformats: (i) traditional channel-based audio (as discussed above), whichis meant to be played through loudspeakers at pre-specified positions;(ii) object-based audio, which involves discrete pulse-code-modulation(PCM) data for single audio objects with associated metadata containingtheir location coordinates (amongst other information); and (iii)scene-based audio, which involves representing the sound field usingcoefficients of spherical harmonic basis functions (also called“spherical harmonic coefficients” or SCH, “Higher-order Ambitions” orHOA, and “HOA coefficients”). The future MPEG encoder may be describedin more detail in a document entitled “Call for Proposals for 3D Audio,”by the International Organization for Standardization/InternationalElectrotechnical Commission (ISO)/(IEC) JTC1/SC29/WG11/N13411, releasedJanuary 2013 in Geneva, Switzerland, and available athttp://mpeg.chiariglione.org/sites/default/files/files/standards/parts/docs/w13411.zip.

There are various ‘surround-sound’ channel-based formats in the market.They range, for example, from the 5.1 home theatre system (which hasbeen the most successful in terms of making inroads into living roomsbeyond stereo) to the 22.2 system developed by NHK (Nippon Hoso Kyokaior Japan Broadcasting Corporation). Content creators (e.g., Hollywoodstudios) would like to produce the soundtrack for a movie once, and notspend effort to remix it for each speaker configuration. Recently,Standards Developing Organizations have been considering ways in whichto provide an encoding into a standardized bitstream and a subsequentdecoding that is adaptable and agnostic to the speaker geometry (andnumber) and acoustic conditions at the location of the playback(involving a renderer).

To provide such flexibility for content creators, a hierarchical set ofelements may be used to represent a sound field. The hierarchical set ofelements may refer to a set of elements in which the elements areordered such that a basic set of lower-ordered elements provides a fullrepresentation of the modeled sound field. As the set is extended toinclude higher-order elements, the representation becomes more detailed,increasing resolution.

One example of a hierarchical set of elements is a set of sphericalharmonic coefficients (SCH). The following expression demonstrates adescription or representation of a sound field using SCH:

${{p_{i}\left( {t,r_{r},\theta_{r},\phi_{r}} \right)} = {\sum\limits_{\omega = 0}^{\infty}\; {\left\lbrack {4\pi {\sum\limits_{n = 0}^{\infty}\; {{j_{n}\left( {kr}_{r} \right)}{\sum\limits_{m = {- n}}^{n}\; {{A_{n}^{m}(k)}{Y_{n}^{m}\left( {\theta_{r},\phi_{r}} \right)}}}}}} \right\rbrack ^{{j\omega}\; t}}}},$

The expression shows that the pressure p_(i) at any point {r_(r), θ_(r),φ_(r)} of the sound field, at time t, can be represented uniquely by theSCH, A_(n) ^(m)(k). Here,

${k = \frac{\omega}{c}},$

c is the speed of sound (˜343 m/s), {r_(r), θ_(r), φ_(r)} is a point ofreference (or observation point), j_(n)(·) is the spherical Besselfunction of order n, and Y_(n) ^(m)(θ_(r), φ_(r)) are the sphericalharmonic basis functions of order n and suborder m. It can be recognizedthat the term in square brackets is a frequency-domain representation ofthe signal (i.e., S(ω, r_(r), θ_(r), φ_(r))) which can be approximatedby various time-frequency transformations, such as the discrete Fouriertransform (DFT), the discrete cosine transform (DCT), or a wavelettransform. Other examples of hierarchical sets include sets of wavelettransform coefficients and other sets of coefficients of multiresolutionbasis functions.

Video data is often displayed in conjunction with corresponding,synchronized audio data, with the audio data typically being generatedto match the perspective of the video data. For example, during framesof video that show a close-up perspective of two people talking in arestaurant, the conversation of the two people may be loud and clearrelative to any background noise at the restaurant such as theconversations of other diners, kitchen noise, background music, etc.During frames of video showing a more distant perspective of the twopeople talking, the conversation of the two people may be less loud andless clear relative to the background noises, the sources of which maynow be in the frame of video.

Traditionally, decisions regarding perspective (e.g. zooming in and outof a scene or panning around a scene) are made by a content producerwith an end consumer of the content having little or no ability to alterthe perspective chosen by the original content producer. It is becomingmore common, however, for users to have some level of control over theperspective they see when watching video. As one example, during afootball broadcast, a user may receive a video feed showing a largesection of the field but may have the ability to zoom in on a specificplayer or group of players. This disclosure introduces techniques foradapting the perception of an audio reproduction in a manner thatmatches a change in the perception of corresponding video. For example,if while watching a football game a user zooms in on the quarterback,the audio may also be adapted to produce an audio effect of zooming inon the quarterback.

A user's perception of video may also change depending on the size ofthe display being used to playback the video. For example, when watchinga movie on a 10-inch tablet, the entire display may be within theviewer's central vision, while when watching the same movie on a100-inch television, the outside portions of the display may only bewithin the viewer's peripheral vision. This disclosure introducestechniques for adapting the perception of an audio reproduction based onthe size of a display being used for the corresponding video data.

The MPEG-H 3D audio bitstream contains new bitfields to signalinformation of a reference screen size used during the contentproduction process. An MPEG-H 3D-compliant audio decoder, severalexamples of which will be described in this disclosure, may also beconfigured to determine an actual screen size of the display setup beingused in conjunction with video corresponding to the audio being decoded.Consequently, according to the techniques of this disclosure, an audiodecoder may adapt the HOA sound field, based on the reference screensize and the actual screen size, so that screen related audio content isbeing perceived from the same location being shown in the video.

This disclosure describes techniques for how HOA soundfields can beadjusted to ensure spatial alignment of the acoustic elements to thevisual component in a mixed audio/video reproduction scenario. Thetechniques of this disclosure may be utilized to help create a coherentaudio/video experience for HOA-only content or for content with acombination of HOA and audio objects where currently only screen-relatedaudio objects are adjusted.

FIG. 1 is a diagram illustrating spherical harmonic basis functions fromthe zero order (n=0) to the fourth order (n=4). As can be seen, for eachorder, there is an expansion of suborders m which are shown but notexplicitly noted in the example of FIG. 1 for ease of illustrationpurposes.

The SCH A_(n) ^(m)(k) can either be physically acquired (e.g., recorded)by various microphone array configurations or, alternatively, they canbe derived from channel-based or object-based descriptions of the soundfield. The SCH represent scene-based audio, where the SCH may be inputto an audio encoder to obtain encoded SCH that may promote moreefficient transmission or storage. For example, a fourth-orderrepresentation involving (1+4)² (25, and hence fourth order)coefficients may be used.

As noted above, the SCH may be derived from a microphone recording usinga microphone array. Various examples of how SCH may be derived frommicrophone arrays are described in Poletti, M., “Three-DimensionalSurround Sound Systems Based on Spherical Harmonics,” J. Audio Eng.Soc., Vol. 53, No. 11, 2005 November, pp. 1004-1025.

To illustrate how the SHCs may be derived from an object-baseddescription, consider the following equation. The coefficients A_(n)^(m)(k) for the sound field corresponding to an individual audio objectmay be expressed as:

A _(n) ^(m)(k)=g(ω)(−4πik)h _(n) ⁽²⁾(kr _(s))Y _(n) ^(m)*(θ_(s), φ_(s)),

where i is √{square root over (−1)}, h_(n) ⁽²⁾ (·) is the sphericalHankel function (of the second kind) of order n, and {r_(s), θ_(s),φ_(s)} is the location of the object. Knowing the object source energy g(ω) as a function of frequency (e.g., using time-frequency analysistechniques, such as performing a fast Fourier transform on the PCMstream) allows us to convert each PCM object and the correspondinglocation into the SCH A_(n) ^(m)(k). Further, it can be shown (since theabove is a linear and orthogonal decomposition) that the A_(n) ^(m)(k)coefficients for each object are additive. In this manner, a multitudeof PCM objects can be represented by the A_(n) ^(m)(k) coefficients(e.g., as a sum of the coefficient vectors for the individual objects).Essentially, the coefficients contain information about the sound field(the pressure as a function of 3D coordinates), and the above representsthe transformation from individual objects to a representation of theoverall sound field, in the vicinity of the observation point {r_(r),θ_(r), φ_(r)}. The remaining figures are described below in the contextof object-based and SCH-based audio coding.

FIG. 2 is a diagram illustrating a system 10 that may perform variousaspects of the techniques described in this disclosure. As shown in theexample of FIG. 2, the system 10 includes a content creator device 12and a content consumer device 14. While described in the context of thecontent creator device 12 and the content consumer device 14, thetechniques may be implemented in any context in which SHCs (which mayalso be referred to as HOA coefficients) or any other hierarchicalrepresentation of a sound field are encoded to form a bitstreamrepresentative of the audio data. Moreover, the content creator device12 may represent any form of computing device capable of implementingthe techniques described in this disclosure, including a handset (orcellular phone), a tablet computer, a smart phone, or a desktop computerto provide a few examples. Likewise, the content consumer device 14 mayrepresent any form of computing device capable of implementing thetechniques described in this disclosure, including a handset (orcellular phone), a tablet computer, a smart phone, a set-top box, astandalone receiver (e.g., a “receiver device”), a television (e.g. a“smart TV”) or a desktop computer to provide a few examples.

The content creator device 12 may be operated by a movie studio or otherentity that may generate multi-channel audio content for consumption byoperators of content consumer devices, such as the content consumerdevice 14. In some examples, the content creator device 12 may beoperated by an individual user who would like to generate an audiosignal with compress HOA coefficients 11 and also include in the audiosignal, one or more field of view (FOV) parameters. Often, the contentcreator generates audio content in conjunction with video content. TheFOV parameters may, for example, describe a reference screen size forthe video content. The content consumer device 14 may be operated by anindividual. The content consumer device 14 may include an audio playbacksystem 16, which may refer to any form of audio playback system capableof rendering SCH for play back as multi-channel audio content.

The content creator device 12 includes an audio editing system 18. Thecontent creator device 12 obtain live recordings 7 in various formats(including directly as HOA coefficients) and audio objects 9, which thecontent creator device 12 may edit using audio editing system 18. Amicrophone 5 may capture the live recordings 7. The content creator may,during the editing process, render HOA coefficients 11 from audioobjects 9, listening to the rendered speaker feeds in an attempt toidentify various aspects of the sound field that require furtherediting. The content creator device 12 may then edit HOA coefficients 11(potentially indirectly through manipulation of different ones of theaudio objects 9 from which the source HOA coefficients may be derived inthe manner described above) and the FOV parameters 13. The contentcreator device 12 may employ the audio editing system 18 to generate theHOA coefficients 11 and FOV parameters 13. The audio editing system 18represents any system capable of editing audio data and outputting theaudio data as one or more source spherical harmonic coefficients.

When the editing process is complete, the content creator device 12 maygenerate audio bitstream 21 based on the HOA coefficients 11. That is,the content creator device 12 includes an audio encoding device 20 thatrepresents a device configured to encode or otherwise compress HOAcoefficients 11 in accordance with various aspects of the techniquesdescribed in this disclosure to generate the audio bitstream 21. Audioencoding device 20 may include, in the audio bitstream 21, values forsignaling FOV parameters 13. The audio encoding device 20 may generatethe audio bitstream 21 for transmission, as one example, across atransmission channel, which may be a wired or wireless channel, a datastorage device, or the like. The audio bitstream 21 may represent anencoded version of the HOA coefficients 11 and may include a primarybitstream and another side bitstream, which may be referred to as sidechannel information. In some examples, audio encoding device 20 mayinclude FOV parameters 13 in the side channel, while in other examples,audio encoding device 20 may include FOV parameters 13 elsewhere. Instill other examples, audio encoding device 20 may not encode FOVparameters 13, and instead, audio playback system 16 may assign defaultvalues to FOV parameters 13′.

While shown in FIG. 2 as being directly transmitted to the contentconsumer device 14, the content creator device 12 may output the audiobitstream 21 to an intermediate device positioned between the contentcreator device 12 and the content consumer device 14. The intermediatedevice may store the audio bitstream 21 for later delivery to thecontent consumer device 14, which may request the bitstream. Theintermediate device may comprise a file server, a web server, a desktopcomputer, a laptop computer, a tablet computer, a mobile phone, a smartphone, a standalone receiver (such as a receiver device), a set-top box,a television (e.g., an integrated display and speaker device, which may,in some examples, be a “smart TV”) or any other device capable ofstoring the audio bitstream 21 for later retrieval by an audio decoder.The intermediate device may reside in a content delivery network capableof streaming the audio bitstream 21 (and possibly in conjunction withtransmitting a corresponding video data bitstream) to subscribers, suchas the content consumer device 14, requesting the audio bitstream 21.

Alternatively, the content creator device 12 may store the audiobitstream 21 to a storage medium, such as a compact disc, a digitalvideo disc, a high definition video disc or other storage media, most ofwhich are capable of being read by a computer and therefore may bereferred to as computer-readable storage media or non-transitorycomputer-readable storage media. In this context, the transmissionchannel may refer to the channels by which content stored to the mediumsare transmitted (and may include retail stores and other store-baseddelivery mechanism). In any event, the techniques of this disclosureshould not therefore be limited in this respect to the example of FIG.2.

Content creator device 12 may further be configured to generate andencode video data 23, and content consumer device 14 may be configuredto receive and decode video data 23. Video data 23 may be associatedwith and transmitted with audio bitstream 21. In this regard, contentcreator device 12 and content consumer device 14 may include additionalhardware and software not explicitly shown in FIG. 2. Content creatordevice 12 may, for example, include cameras for acquiring video data, avideo editing system for editing the video data, and a video encoder forencoding the video data, and content consumer device 14 may also includea video decoder and video renderer.

As further shown in the example of FIG. 2, the content consumer device14 includes the audio playback system 16. The audio playback system 16may represent any audio playback system capable of playing backmulti-channel audio data. The audio playback system 16 may include anumber of different renderers 22. The renderers 22 may each provide fora different form of rendering, where the different forms of renderingmay include one or more of the various ways of performing vector-baseamplitude panning (VBAP), and/or one or more of the various ways ofperforming sound field synthesis. As used herein, “A and/or B” means “Aor B”, or both “A and B”.

The audio playback system 16 may further include an audio decodingdevice 24. The audio decoding device 24 may represent a deviceconfigured to decode HOA coefficients 11′ and FOV parameters 13′ fromthe audio bitstream 21, where the HOA coefficients 11′ may be similar tothe HOA coefficients 11 but differ due to lossy operations (e.g.,quantization) and/or transmission via the transmission channel. FOVparameters 13, by contrast, may be losslessly coded. The audio playbacksystem 16 may, after decoding the audio bitstream 21 to obtain the HOAcoefficients 11′ and render the HOA coefficients 11′ to outputloudspeaker feeds 25. As will be explained in more detail below, themanner in which audio playback system 16 renders HOA coefficients 11′may be, in some instances, modified based on FOV parameters 13′ inconjunction with FOV parameters of display 15. The loudspeaker feeds 25may drive one or more loudspeakers (which are not shown in the exampleof FIG. 2 for ease of illustration purposes). The loudspeakers may beconfigured to output a rendered audio signal, such as a rendered audiosignal represented by loudspeaker feeds 25.

To select the appropriate renderer or, in some instances, generate anappropriate renderer, the audio playback system 16 may obtainloudspeaker information 13 indicative of a number of loudspeakers and/ora spatial geometry of the loudspeakers. In some instances, the audioplayback system 16 may obtain the loudspeaker information 13 using areference microphone and driving the loudspeakers in such a manner as todynamically determine the loudspeaker information 13. In other instancesor in conjunction with the dynamic determination of the loudspeakerinformation 13, the audio playback system 16 may prompt a user tointerface with the audio playback system 16 and input the loudspeakerinformation 13.

The audio playback system 16 may then select one of the audio renderers22 based on the loudspeaker information 13. In some instances, the audioplayback system 16 may, when none of the audio renderers 22 are withinsome threshold similarity measure (in terms of the loudspeaker geometry)to the loudspeaker geometry specified in the loudspeaker information 13,generate the one of audio renderers 22 based on the loudspeakerinformation 13. The audio playback system 16 may, in some instances,generate one of the audio renderers 22 based on the loudspeakerinformation 13 without first attempting to select an existing one of theaudio renderers 22. One or more speakers 3 may then playback therendered loudspeaker feeds 25.

As shown in FIG. 2, content consumer device 14 also has an associateddisplay device, display 15. In the example of FIG. 2, display 15 isshown as being incorporated into content consumer device 14; however, inother examples, display 15 may be external to content consumer device14. As will be explained in more detail below, display 15 may have oneor more associated FOV parameters that are separate from FOV parameters13′. FOV parameters 13′ represent parameters associated with a referencescreen at the time of content creation, while the FOV parameters ofdisplay 15 are FOV parameters of a viewing window used for playback.Audio playback system 16 may modify or generate one of audio renderer 22based on both FOV parameters 13′ and the FOV parameters associated withdisplay 15.

FIG. 3 is a block diagram illustrating, in more detail, one example ofthe audio encoding device 20 shown in the example of FIG. 2 that mayperform various aspects of the techniques described in this disclosure.The audio encoding device 20 includes a content analysis unit 26, avector-based decomposition unit 27 and a directional-based decompositionunit 28. Although described briefly below, more information regardingthe audio encoding device 20 and the various aspects of compressing orotherwise encoding HOA coefficients is available in International PatentApplication Publication No. WO 2014/194099, entitled “INTERPOLATION FORDECOMPOSED REPRESENTATIONS OF A SOUND FIELD,” filed 29 May, 2014.

The content analysis unit 26 represents a unit configured to analyze thecontent of the HOA coefficients 11 to identify whether the HOAcoefficients 11 represent content generated from a live recording or anaudio object. The content analysis unit 26 may determine whether the HOAcoefficients 11 were generated from a recording of an actual sound fieldor from an artificial audio object. In some instances, when the framedHOA coefficients 11 were generated from a recording, the contentanalysis unit 26 passes the HOA coefficients 11 to the vector-baseddecomposition unit 27. In some instances, when the framed HOAcoefficients 11 were generated from a synthetic audio object, thecontent analysis unit 26 passes the HOA coefficients 11 to thedirectional-based decomposition unit 28. The directional-baseddecomposition unit 28 may represent a unit configured to perform adirectional-based synthesis of the HOA coefficients 11 to generate adirectional-based bitstream 21.

As shown in the example of FIG. 3, the vector-based decomposition unit27 may include a linear invertible transform (LIT) unit 30, a parametercalculation unit 32, a reorder unit 34, a foreground selection unit 36,an energy compensation unit 38, a psychoacoustic audio coder unit 40, abitstream generation unit 42, a sound field analysis unit 44, acoefficient reduction unit 46, a background (BG) selection unit 48, aspatio-temporal interpolation unit 50, and a quantization unit 52.

The linear invertible transform (LIT) unit 30 receives the HOAcoefficients 11 in the form of HOA channels, each channel representativeof a block or frame of a coefficient associated with a given order,sub-order of the spherical basis functions (which may be denoted asHOA[k], where k may denote the current frame or block of samples). Thematrix of HOA coefficients 11 may have dimensions D: M×(N+1)².

The LIT unit 30 may represent a unit configured to perform a form ofanalysis referred to as singular value decomposition. While describedwith respect to SVD, the techniques described in this disclosure may beperformed with respect to any similar transformation or decompositionthat provides for sets of linearly uncorrelated, energy compactedoutput. Also, reference to “sets” in this disclosure is generallyintended to refer to non-zero sets unless specifically stated to thecontrary and is not intended to refer to the classical mathematicaldefinition of sets that includes the so-called “empty set.” Analternative transformation may comprise a principal component analysis,which is often referred to as “PCA.” Depending on the context, PCA maybe referred to by a number of different names, such as discreteKarhunen-Loeve transform, the Hotelling transform, proper orthogonaldecomposition (POD), and eigenvalue decomposition (EVD) to name a fewexamples. Properties of such operations that are conducive to theunderlying goal of compressing audio data are ‘energy compaction’ and‘decorrelation’ of the multichannel audio data.

In any event, assuming the LIT unit 30 performs a singular valuedecomposition (which, again, may be referred to as “SVD”) for purposesof example, the LIT unit 30 may transform the HOA coefficients 11 intotwo or more sets of transformed HOA coefficients. The “sets” oftransformed HOA coefficients may include vectors of transformed HOAcoefficients. In the example of FIG. 3, the LIT unit 30 may perform theSVD with respect to the HOA coefficients 11 to generate a so-called Vmatrix, an S matrix, and a U matrix. SVD, in linear algebra, mayrepresent a factorization of a y-by-z real or complex matrix X (where Xmay represent multi-channel audio data, such as the HOA coefficients 11)in the following form:

X=USV*

U may represent a y-by-y real or complex unitary matrix, where the ycolumns of U are known as the left-singular vectors of the multi-channelaudio data. S may represent a y-by-z rectangular diagonal matrix withnon-negative real numbers on the diagonal, where the diagonal values ofS are known as the singular values of the multi-channel audio data. V*(which may denote a conjugate transpose of V) may represent a z-by-zreal or complex unitary matrix, where the z columns of V* are known asthe right-singular vectors of the multi-channel audio data.

In some examples, the V* matrix in the SVD mathematical expressionreferenced above is denoted as the conjugate transpose of the V matrixto reflect that SVD may be applied to matrices comprising complexnumbers. When applied to matrices comprising only real-numbers, thecomplex conjugate of the V matrix (or, in other words, the V* matrix)may be considered to be the transpose of the V matrix. Below it isassumed, for ease of illustration purposes, that the HOA coefficients 11comprise real-numbers with the result that the V matrix is outputthrough SVD rather than the V* matrix. Moreover, while denoted as the Vmatrix in this disclosure, reference to the V matrix should beunderstood to refer to the transpose of the V matrix where appropriate.While assumed to be the V matrix, the techniques may be applied in asimilar fashion to HOA coefficients 11 having complex coefficients,where the output of the SVD is the V* matrix. Accordingly, thetechniques should not be limited in this respect to only provide forapplication of SVD to generate a V matrix, but may include applicationof SVD to HOA coefficients 11 having complex components to generate a V*matrix.

In this way, the LIT unit 30 may perform SVD with respect to the HOAcoefficients 11 to output US[k] vectors 33 (which may represent acombined version of the S vectors and the U vectors) having dimensionsD: M×(N+1)², and V[k] vectors 35 having dimensions D: (N+1)² ×(N+1)².Individual vector elements in the US[k] matrix may also be termedX_(PS)(k) while individual vectors of the V[k] matrix may also be termedv(k)

An analysis of the U, S and V matrices may reveal that the matricescarry or represent spatial and temporal characteristics of theunderlying sound field represented above by X. Each of the N vectors inU (of length M samples) may represent normalized separated audio signalsas a function of time (for the time period represented by M samples),that are orthogonal to each other and that have been decoupled from anyspatial characteristics (which may also be referred to as directionalinformation). The spatial characteristics, representing spatial shapeand position (r, theta, phi) may instead be represented by individuali^(the) vectors, v^((i))(k), in the V matrix (each of length (N+1)²).The individual elements of each of v^((i))(k) vectors may represent anHOA coefficient describing the shape (including width) and position ofthe sound field for an associated audio object. Both the vectors in theU matrix and the V matrix are normalized such that theirroot-mean-square energies are equal to unity. The energy of the audiosignals in U are thus represented by the diagonal elements in S.Multiplying U and S to form US[k] (with individual vector elementsX_(PS)(k)), thus represent the audio signal with energies. The abilityof the SVD decomposition to decouple the audio time-signals (in U),their energies (in S) and their spatial characteristics (in V) maysupport various aspects of the techniques described in this disclosure.Further, the model of synthesizing the underlying HOA[k] coefficients,X, by a vector multiplication of US[k] and V[k] gives rise the term“vector-based decomposition,” which is used throughout this document.

Although described as being performed directly with respect to the HOAcoefficients 11, the LIT unit 30 may apply the linear invertibletransform to derivatives of the HOA coefficients 11. For example, theLIT unit 30 may apply SVD with respect to a power spectral densitymatrix derived from the HOA coefficients 11. By performing SVD withrespect to the power spectral density (PSD) of the HOA coefficientsrather than the coefficients themselves, the LIT unit 30 may potentiallyreduce the computational complexity of performing the SVD in terms ofone or more of processor cycles and storage space, while achieving thesame source audio encoding efficiency as if the SVD were applieddirectly to the HOA coefficients.

The parameter calculation unit 32 represents a unit configured tocalculate various parameters, such as a correlation parameter (R),directional properties parameters (θ, φ, r), and an energy property (e).Each of the parameters for the current frame may be denoted as R[k],θ[k], φ[k], r[k] and e[k]. The parameter calculation unit 32 may performan energy analysis and/or correlation (or so-called cross-correlation)with respect to the US[k] vectors 33 to identify the parameters. Theparameter calculation unit 32 may also determine the parameters for theprevious frame, where the previous frame parameters may be denotedR[k-1], θ[k-1],φ[k-1], r[k-1] and e[k-1], based on the previous frame ofUS[k-1] vector and V[k-1] vectors. The parameter calculation unit 32 mayoutput the current parameters 37 and the previous parameters 39 toreorder unit 34.

The parameters calculated by the parameter calculation unit 32 may beused by the reorder unit 34 to re-order the audio objects to representtheir natural evaluation or continuity over time. The reorder unit 34may compare each of the parameters 37 from the first US[k] vectors 33turn-wise against each of the parameters 39 for the second US[k-1]vectors 33. The reorder unit 34 may reorder (using, as one example, aHungarian algorithm) the various vectors within the US[k] matrix 33 andthe V[k] matrix 35 based on the current parameters 37 and the previousparameters 39 to output a reordered US[k] matrix 33′ (which may bedenoted mathematically as US[k]) and a reordered V[k] matrix 35′ (whichmay be denoted mathematically as V[k]) to a foreground sound (orpredominant sound—PS) selection unit 36 (“foreground selection unit 36”)and an energy compensation unit 38.

The sound field analysis unit 44 may represent a unit configured toperform a sound field analysis with respect to the HOA coefficients 11so as to potentially achieve a target bitrate 41. The sound fieldanalysis unit 44 may, based on the analysis and/or on a received targetbitrate 41, determine the total number of psychoacoustic coderinstantiations (which may be a function of the total number of ambientor background channels (BG_(TOT)) and the number of foreground channelsor, in other words, predominant channels. The total number ofpsychoacoustic coder instantiations can be denoted asnumHOATransportChannels.

The sound field analysis unit 44 may also determine, again topotentially achieve the target bitrate 41, the total number offoreground channels (nFG) 45, the minimum order of the background (or,in other words, ambient) sound field (NBG or, alternatively,MinAmbHOAorder), the corresponding number of actual channelsrepresentative of the minimum order of background sound field(nBGa=(MinAmbHOAorder+1)²), and indices (i) of additional BG HOAchannels to send (which may collectively be denoted as backgroundchannel information 43 in the example of FIG. 3). The background channelinformation 42 may also be referred to as ambient channel information43. Each of the channels that remains from numHOATransportChannels—nBGa,may either be an “additional background/ambient channel”, an “activevector-based predominant channel”, an “active directional basedpredominant signal” or “completely inactive”. In one aspect, the channeltypes may be indicated (as a “ChannelType”) syntax element by two bits(e.g. 00: directional based signal; 01: vector-based predominant signal;10: additional ambient signal; 11: inactive signal). The total number ofbackground or ambient signals, nBGa, may be given by (MinAmbHOAorder+1)²+the number of times the index 10 (in the above example) appears as achannel type in the bitstream for that frame.

The sound field analysis unit 44 may select the number of background(or, in other words, ambient) channels and the number of foreground (or,in other words, predominant) channels based on the target bitrate 41,selecting more background and/or foreground channels when the targetbitrate 41 is relatively higher (e.g., when the target bitrate 41 equalsor is greater than 512 Kbps). In one aspect, the numHOATransportChannelsmay be set to 8 while the MinAmbHOAorder may be set to 1 in the headersection of the bitstream. In this scenario, at every frame, fourchannels may be dedicated to represent the background or ambient portionof the sound field while the other 4 channels can, on a frame-by-framebasis vary on the type of channel—e.g., either used as an additionalbackground/ambient channel or a foreground/predominant channel. Theforeground/predominant signals can be one of either vector-based ordirectional based signals, as described above.

In some instances, the total number of vector-based predominant signalsfor a frame, may be given by the number of times the ChannelType indexis 01 in the bitstream of that frame. In the above aspect, for everyadditional background/ambient channel (e.g., corresponding to aChannelType of 10), corresponding information of which of the possibleHOA coefficients (beyond the first four) may be represented in thatchannel. The information, for fourth order HOA content, may be an indexto indicate the HOA coefficients 5-25. The first four ambient HOAcoefficients 1-4 may be sent all the time when minAmbHOAorder is set to1, hence the audio encoding device may only need to indicate one of theadditional ambient HOA coefficient having an index of 5-25. Theinformation could thus be sent using a 5 bits syntax element (for4^(the) order content), which may be denoted as “CodedAmbCoeffldx.” Inany event, the sound field analysis unit 44 outputs the backgroundchannel information 43 and the HOA coefficients 11 to the background(BG) selection unit 36, the background channel information 43 tocoefficient reduction unit 46 and the bitstream generation unit 42, andthe nFG 45 to a foreground selection unit 36.

The background selection unit 48 may represent a unit configured todetermine background or ambient HOA coefficients 47 based on thebackground channel information (e.g., the background sound field(N_(BG)) and the number (nBGa) and the indices (i) of additional BG HOAchannels to send). For example, when NBG equals one, the backgroundselection unit 48 may select the HOA coefficients 11 for each sample ofthe audio frame having an order equal to or less than one. Thebackground selection unit 48 may, in this example, then select the HOAcoefficients 11 having an index identified by one of the indices (i) asadditional BG HOA coefficients, where the nBGa is provided to thebitstream generation unit 42 to be specified in the audio bitstream 21so as to enable the audio decoding device, such as the audio decodingdevice 24 shown in the example of FIGS. 2 and 4, to parse the backgroundHOA coefficients 47 from the audio bitstream 21. The backgroundselection unit 48 may then output the ambient HOA coefficients 47 to theenergy compensation unit 38. The ambient HOA coefficients 47 may havedimensions D: M×[(N_(BG)+1)² +nBGa]. The ambient HOA coefficients 47 mayalso be referred to as “ambient HOA coefficients 47, ” where each of theambient HOA coefficients 47 corresponds to a separate ambient HOAchannel 47 to be encoded by the psychoacoustic audio coder unit 40.

The foreground selection unit 36 may represent a unit configured toselect the reordered US[k] matrix 33′ and the reordered V[k] matrix 35′that represent foreground or distinct components of the sound fieldbased on nFG 45 (which may represent a one or more indices identifyingthe foreground vectors). The foreground selection unit 36 may output nFGsignals 49 (which may be denoted as a reordered US[k]_(1, . . . , nFG)49, FG_(1, . . . , nfG)[k] 49, or X_(PS) ^((1 . . . nFG)) (k) 49) to thepsychoacoustic audio coder unit 40, where the nFG signals 49 may havedimensions D: M×nFG and each represent mono-audio objects. Theforeground selection unit 36 may also output the reordered V[k] matrix35′ (or v^((1 . . . nFG)) (k) 35′) corresponding to foregroundcomponents of the sound field to the spatio-temporal interpolation unit50, where a subset of the reordered V[k] matrix 35′ corresponding to theforeground components may be denoted as foreground V[k] matrix 51 _(k)(which may be mathematically denoted as V _(1, . . . , n FG)[k]) havingdimensions D: (N+1)² x nFG.

The energy compensation unit 38 may represent a unit configured toperform energy compensation with respect to the ambient HOA coefficients47 to compensate for energy loss due to removal of various ones of theHOA channels by the background selection unit 48. The energycompensation unit 38 may perform an energy analysis with respect to oneor more of the reordered US[k] matrix 33′, the reordered V[k] matrix35′, the nFG signals 49, the foreground V[k] vectors 51 _(k) and theambient HOA coefficients 47 and then perform energy compensation basedon the energy analysis to generate energy compensated ambient HOAcoefficients 47′. The energy compensation unit 38 may output the energycompensated ambient HOA coefficients 47′ to the psychoacoustic audiocoder unit 40.

The spatio-temporal interpolation unit 50 may represent a unitconfigured to receive the foreground V[k] vectors 51 _(k) for thek^(the) frame and the foreground V[k-1] vectors 51 _(k-)1 for theprevious frame (hence the k-1 notation) and perform spatio-temporalinterpolation to generate interpolated foreground V[k] vectors. Thespatio-temporal interpolation unit 50 may recombine the nFG signals 49with the foreground V[k] vectors 51 _(k) to recover reordered foregroundHOA coefficients. The spatio-temporal interpolation unit 50 may thendivide the reordered foreground HOA coefficients by the interpolatedV[k] vectors to generate interpolated nFG signals 49′. Thespatio-temporal interpolation unit 50 may also output the foregroundV[k] vectors 51 _(k) that were used to generate the interpolatedforeground V[k] vectors so that an audio decoding device, such as theaudio decoding device 24, may generate the interpolated foreground V[k]vectors and thereby recover the foreground V[k] vectors 51 _(k). Theforeground V[k] vectors 51 _(k) used to generate the interpolatedforeground V[k] vectors are denoted as the remaining foreground V[k]vectors 53. In order to ensure that the same V[k] and V[k-1] are used atthe encoder and decoder (to create the interpolated vectors V[k])quantized/dequantized versions of the vectors may be used at the encoderand decoder. The spatio-temporal interpolation unit 50 may output theinterpolated nFG signals 49′ to the psychoacoustic audio coder unit 46and the interpolated foreground V[k] vectors 51 _(k) to the coefficientreduction unit 46.

The coefficient reduction unit 46 may represent a unit configured toperform coefficient reduction with respect to the remaining foregroundV[k] vectors 53 based on the background channel information 43 to outputreduced foreground V[k] vectors 55 to the quantization unit 52. Thereduced foreground V[k] vectors 55 may have dimensions D:[(N+1)²−(NBG+1)²-BG_(TOT)]×nFG. The coefficient reduction unit 46 may,in this respect, represent a unit configured to reduce the number ofcoefficients in the remaining foreground V[k] vectors 53. In otherwords, coefficient reduction unit 46 may represent a unit configured toeliminate the coefficients in the foreground V[k] vectors (that form theremaining foreground V[k] vectors 53) having little to no directionalinformation. In some examples, the coefficients of the distinct or, inother words, foreground V[k] vectors corresponding to a first and zeroorder basis functions (which may be denoted as N_(BG)) provide littledirectional information and therefore can be removed from the foregroundV-vectors (through a process that may be referred to as “coefficientreduction”). In this example, greater flexibility may be provided to notonly identify the coefficients that correspond N_(BG) but to identifyadditional HOA channels (which may be denoted by the variableTotalOfAddAmbHOAChan) from the set of [(N_(BG)+1)²+1, (N+1)²].

The quantization unit 52 may represent a unit configured to perform anyform of quantization to compress the reduced foreground V[k] vectors 55to generate coded foreground V[k] vectors 57, outputting the codedforeground V[k] vectors 57 to the bitstream generation unit 42. Inoperation, the quantization unit 52 may represent a unit configured tocompress a spatial component of the sound field, i.e., one or more ofthe reduced foreground V[k] vectors 55 in this example. The quantizationunit 52 may perform any one of the following 12 quantization modes, asindicated by a quantization mode syntax element denoted “NbitsQ”:

NbitsQ value Type of Quantization Mode 0-3: Reserved 4: VectorQuantization 5: Scalar Quantization without Huffman Coding 6: 6-bitScalar Quantization with Huffman Coding 7: 7-bit Scalar Quantizationwith Huffman Coding 8: 8-bit Scalar Quantization with Huffman Coding . .. . . . 16:  16-bit Scalar Quantization with Huffman Coding

The quantization unit 52 may also perform predicted versions of any ofthe foregoing types of quantization modes, where a difference isdetermined between an element of (or a weight when vector quantizationis performed) of the V-vector of a previous frame and the element (orweight when vector quantization is performed) of the V-vector of acurrent frame is determined. The quantization unit 52 may then quantizethe difference between the elements or weights of the current frame andprevious frame rather than the value of the element of the V-vector ofthe current frame itself.

The quantization unit 52 may perform multiple forms of quantization withrespect to each of the reduced foreground V[k] vectors 55 to obtainmultiple coded versions of the reduced foreground V[k] vectors 55. Thequantization unit 52 may select the one of the coded versions of thereduced foreground V[k] vectors 55 as the coded foreground V[k] vector57.l The quantization unit 52 may, in other words, select one of thenon-predicted vector-quantized V-vector, predicted vector-quantizedV-vector, the non-Huffman-coded scalar-quantized V-vector, and theHuffman-coded scalar-quantized V-vector to use as the outputswitched-quantized V-vector based on any combination of the criteriadiscussed in this disclosure. In some examples, the quantization unit 52may select a quantization mode from a set of quantization modes thatincludes a vector quantization mode and one or more scalar quantizationmodes, and quantize an input V-vector based on (or according to) theselected mode. The quantization unit 52 may then provide the selectedone of the non-predicted vector-quantized V-vector (e.g., in terms ofweight values or bits indicative thereof), predicted vector-quantizedV-vector (e.g., in terms of error values or bits indicative thereof),the non-Huffman-coded scalar-quantized V-vector and the Huffman-codedscalar-quantized V-vector to the bitstream generation unit 52 as thecoded foreground V[k] vectors 57. The quantization unit 52 may alsoprovide the syntax elements indicative of the quantization mode (e.g.,the NbitsQ syntax element) and any other syntax elements used todequantize or otherwise reconstruct the V-vector.

The psychoacoustic audio coder unit 40 included within the audioencoding device 20 may represent multiple instances of a psychoacousticaudio coder, each of which is used to encode a different audio object orHOA channel of each of the energy compensated ambient HOA coefficients47′ and the interpolated nFG signals 49′ to generate encoded ambient HOAcoefficients 59 and encoded nFG signals 61. The psychoacoustic audiocoder unit 40 may output the encoded ambient HOA coefficients 59 and theencoded nFG signals 61 to the bitstream generation unit 42.

The bitstream generation unit 42 included within the audio encodingdevice 20 represents a unit that formats data to conform to a knownformat (which may refer to a format known by a decoding device), therebygenerating the vector-based bitstream 21. The audio bitstream 21 may, inother words, represent encoded audio data, having been encoded in themanner described above. The bitstream generation unit 42 may represent amultiplexer in some examples, which may receive the coded foregroundV[k] vectors 57, the encoded ambient HOA coefficients 59, the encodednFG signals 61 and the background channel information 43. The bitstreamgeneration unit 42 may then generate audio bitstream 21 based on thecoded foreground V[k] vectors 57, the encoded ambient HOA coefficients59, the encoded nFG signals 61 and the background channel information43. In this way, the bitstream generation unit 42 may thereby specifythe vectors 57 in the audio bitstream 21 to obtain the audio bitstream21. The audio bitstream 21 may include a primary or main bitstream andone or more side channel bitstreams.

Although not shown in the example of FIG. 3, the audio encoding device20 may also include a bitstream output unit that switches the bitstreamoutput from the audio encoding device 20 (e.g., between thedirectional-based bitstream 21 and the vector-based bitstream 21) basedon whether a current frame is to be encoded using the directional-basedsynthesis or the vector-based synthesis. The bitstream output unit mayperform the switch based on the syntax element output by the contentanalysis unit 26 indicating whether a directional-based synthesis wasperformed (as a result of detecting that the HOA coefficients 11 weregenerated from a synthetic audio object) or a vector-based synthesis wasperformed (as a result of detecting that the HOA coefficients wererecorded). The bitstream output unit may specify the correct headersyntax to indicate the switch or current encoding used for the currentframe along with the respective one of the audio bitstreams 21.

Moreover, as noted above, the sound field analysis unit 44 may identifyBGTOT ambient HOA coefficients 47, which may change on a frame-by-framebasis (although at times BG_(TOT) may remain constant or the same acrosstwo or more adjacent (in time) frames). The change in BG_(TOT) mayresult in changes to the coefficients expressed in the reducedforeground V[k] vectors 55. The change in BG_(TOT) may result inbackground HOA coefficients (which may also be referred to as “ambientHOA coefficients”) that change on a frame-by-frame basis (although,again, at times BG_(TOT) may remain constant or the same across two ormore adjacent (in time) frames). The changes often result in a change ofenergy for the aspects of the sound field represented by the addition orremoval of the additional ambient HOA coefficients and the correspondingremoval of coefficients from or addition of coefficients to the reducedforeground V[k] vectors 55.

As a result, the sound field analysis unit 44 may further determine whenthe ambient HOA coefficients change from frame to frame and generate aflag or other syntax element indicative of the change to the ambient HOAcoefficient in terms of being used to represent the ambient componentsof the sound field (where the change may also be referred to as a“transition” of the ambient HOA coefficient or as a “transition” of theambient HOA coefficient). In particular, the coefficient reduction unit46 may generate the flag (which may be denoted as an AmbCoeffTransitionflag or an AmbCoeffldxTransition flag), providing the flag to thebitstream generation unit 42 so that the flag may be included in theaudio bitstream 21 (possibly as part of side channel information).

The coefficient reduction unit 46 may, in addition to specifying theambient coefficient transition flag, also modify how the reducedforeground V[k] vectors 55 are generated. In one example, upondetermining that one of the ambient HOA ambient coefficients is intransition during the current frame, the coefficient reduction unit 46may specify, a vector coefficient (which may also be referred to as a“vector element” or “element”) for each of the V-vectors of the reducedforeground V[k] vectors 55 that corresponds to the ambient HOAcoefficient in transition. Again, the ambient HOA coefficient intransition may add or remove from the BG_(TOT) total number ofbackground coefficients. Therefore, the resulting change in the totalnumber of background coefficients affects whether the ambient HOAcoefficient is included or not included in the bitstream, and whetherthe corresponding element of the V-vectors are included for theV-vectors specified in the bitstream in the second and thirdconfiguration modes described above. More information regarding how thecoefficient reduction unit 46 may specify the reduced foreground V[k]vectors 55 to overcome the changes in energy is provided in U.S.application Ser. No. 14/594,533, entitled “TRANSITIONING OF AMBIENTHIGHER-ORDER AMBITION COEFFICIENTS,” filed Jan. 12, 2015.

FIG. 4 is a block diagram illustrating the audio decoding device 24 ofFIG. 2 in more detail. As shown in the example of FIG. 4 the audiodecoding device 24 may include an extraction unit 72, adirectional-based reconstruction unit 90 and a vector-basedreconstruction unit 92. Although described below, more informationregarding the audio decoding device 24 and the various aspects ofdecompressing or otherwise decoding HOA coefficients is available inInternational Patent Application Publication No. WO 2014/194099,entitled “INTERPOLATION FOR DECOMPOSED REPRESENTATIONS OF A SOUNDFIELD,” filed 29 May, 2014.

The extraction unit 72 may represent a unit configured to receive theaudio bitstream 21 and extract the various encoded versions (e.g., adirectional-based encoded version or a vector-based encoded version) ofthe HOA coefficients 11. The extraction unit 72 may determine from theabove noted syntax element indicative of whether the HOA coefficients 11were encoded via the various direction-based or vector-based versions.When a directional-based encoding was performed, the extraction unit 72may extract the directional-based version of the HOA coefficients 11 andthe syntax elements associated with the encoded version (which isdenoted as directional-based information 91 in the example of FIG. 4),passing the directional-based information 91 to the directional-basedreconstruction unit 90. The directional-based reconstruction unit 90 mayrepresent a unit configured to reconstruct the HOA coefficients in theform of HOA coefficients 11′ based on the directional-based information91. The bitstream and the arrangement of syntax elements within thebitstream is described below in more detail with respect to the exampleof FIGS. 7A-7J.

When the syntax element indicates that the HOA coefficients 11 wereencoded using a vector-based synthesis, the extraction unit 72 mayextract the coded foreground V[k] vectors 57 (which may include codedweights 57 and/or indices 63 or scalar quantized V-vectors), the encodedambient HOA coefficients 59 and the corresponding audio objects 61(which may also be referred to as the encoded nFG signals 61). The audioobjects 61 each correspond to one of the vectors 57. The extraction unit72 may pass the coded foreground V[k] vectors 57 to the V-vectorreconstruction unit 74 and the encoded ambient HOA coefficients 59 alongwith the encoded nFG signals 61 to the psychoacoustic decoding unit 80.

The V-vector reconstruction unit 74 may represent a unit configured toreconstruct the V-vectors from the encoded foreground V[k] vectors 57.The V-vector reconstruction unit 74 may operate in a manner reciprocalto that of the quantization unit 52.

The psychoacoustic decoding unit 80 may operate in a manner reciprocalto the psychoacoustic audio coder unit 40 shown in the example of FIG. 3so as to decode the encoded ambient HOA coefficients 59 and the encodednFG signals 61 and thereby generate energy compensated ambient HOAcoefficients 47′ and the interpolated nFG signals 49′ (which may also bereferred to as interpolated nFG audio objects 49′). The psychoacousticdecoding unit 80 may pass the energy compensated ambient HOAcoefficients 47′ to the fade unit 770 and the nFG signals 49′ to theforeground formulation unit 78.

The spatio-temporal interpolation unit 76 may operate in a mannersimilar to that described above with respect to the spatio-temporalinterpolation unit 50. The spatio-temporal interpolation unit 76 mayreceive the reduced foreground V[k] vectors 55 _(k) and perform thespatio-temporal interpolation with respect to the foreground V[k]vectors 55 _(k) and the reduced foreground V[k-1] vectors 55 _(k-)1 togenerate interpolated foreground V[k] vectors 55 _(k)″. Thespatio-temporal interpolation unit 76 may forward the interpolatedforeground V[k] vectors 55 _(k)″ to the fade unit 770.

The extraction unit 72 may also output a signal 757 indicative of whenone of the ambient HOA coefficients is in transition to fade unit 770,which may then determine which of the SCH_(BG) 47′ (where the SCH_(BG)47′ may also be denoted as “ambient HOA channels 47′” or “ambient HOAcoefficients 47′”) and the elements of the interpolated foreground V[k]vectors 55 _(k)″ are to be either faded-in or faded-out. In someexamples, the fade unit 770 may operate opposite with respect to each ofthe ambient HOA coefficients 47′ and the elements of the interpolatedforeground V[k] vectors 55 _(k)″. That is, the fade unit 770 may performa fade-in or fade-out, or both a fade-in or fade-out with respect tocorresponding one of the ambient HOA coefficients 47′, while performinga fade-in or fade-out or both a fade-in and a fade-out, with respect tothe corresponding one of the elements of the interpolated foregroundV[k] vectors 55 _(k)″. The fade unit 770 may output adjusted ambient HOAcoefficients 47″ to the HOA coefficient formulation unit 82 and adjustedforeground V[k] vectors 55 _(k)″ to the foreground formulation unit 78.In this respect, the fade unit 770 represents a unit configured toperform a fade operation with respect to various aspects of the HOAcoefficients or derivatives thereof, e.g., in the form of the ambientHOA coefficients 47′ and the elements of the interpolated foregroundV[k] vectors 55 _(k)″.

The foreground formulation unit 78 may represent a unit configured toperform matrix multiplication with respect to the adjusted foregroundV[k] vectors 55 _(k)′″ and the interpolated nFG signals 49′ to generatethe foreground HOA coefficients 65. In this respect, the foregroundformulation unit 78 may combine the audio objects 49′ (which is anotherway by which to denote the interpolated nFG signals 49′) with thevectors 55 _(k)′″ to reconstruct the foreground or, in other words,predominant aspects of the HOA coefficients 11′. The foregroundformulation unit 78 may perform a matrix multiplication of theinterpolated nFG signals 49′ by the adjusted foreground V[k] vectors 55_(k)′″.

The HOA coefficient formulation unit 82 may represent a unit configuredto combine the foreground HOA coefficients 65 to the adjusted ambientHOA coefficients 47″ so as to obtain the HOA coefficients 11′. The primenotation reflects that the HOA coefficients 11′ may be similar to butnot the same as the HOA coefficients 11. The differences between the HOAcoefficients 11 and 11′ may result from loss due to transmission over alossy transmission medium, quantization or other lossy operations.

FIG. 5 is a flowchart illustrating exemplary operation of an audioencoding device, such as the audio encoding device 20 shown in theexample of FIG. 3, in performing various aspects of the vector-basedsynthesis techniques described in this disclosure. Initially, the audioencoding device 20 receives the HOA coefficients 11 (106). The audioencoding device 20 may invoke the LIT unit 30, which may apply a LITwith respect to the HOA coefficients to output transformed HOAcoefficients (e.g., in the case of SVD, the transformed HOA coefficientsmay comprise the US[k] vectors 33 and the V[k] vectors 35) (107).

The audio encoding device 20 may next invoke the parameter calculationunit 32 to perform the above described analysis with respect to anycombination of the US[k] vectors 33, US[k-1] vectors 33, the V[k] and/orV[k-1] vectors 35 to identify various parameters in the manner describedabove. That is, the parameter calculation unit 32 may determine at leastone parameter based on an analysis of the transformed HOA coefficients33/35 (108).

The audio encoding device 20 may then invoke the reorder unit 34, whichmay reorder the transformed HOA coefficients (which, again in thecontext of SVD, may refer to the US[k] vectors 33 and the V[k] vectors35) based on the parameter to generate reordered transformed HOAcoefficients 33′/35′ (or, in other words, the US[k] vectors 33′ and theV[k] vectors 35′), as described above (109). The audio encoding device20 may, during any of the foregoing operations or subsequent operations,also invoke the sound field analysis unit 44. The sound field analysisunit 44 may, as described above, perform a sound field analysis withrespect to the HOA coefficients 11 and/or the transformed HOAcoefficients 33/35 to determine the total number of foreground channels(nFG) 45, the order of the background sound field (NBG) and the number(nBGa) and indices (i) of additional BG HOA channels to send (which maycollectively be denoted as background channel information 43 in theexample of FIG. 3) (109).

The audio encoding device 20 may also invoke the background selectionunit 48. The background selection unit 48 may determine background orambient HOA coefficients 47 based on the background channel information43 (110). The audio encoding device 20 may further invoke the foregroundselection unit 36, which may select the reordered US[k] vectors 33′ andthe reordered V[k] vectors 35′ that represent foreground or distinctcomponents of the sound field based on nFG 45 (which may represent a oneor more indices identifying the foreground vectors) (112).

The audio encoding device 20 may invoke the energy compensation unit 38.The energy compensation unit 38 may perform energy compensation withrespect to the ambient HOA coefficients 47 to compensate for energy lossdue to removal of various ones of the HOA coefficients by the backgroundselection unit 48 (114) and thereby generate energy compensated ambientHOA coefficients 47′.

The audio encoding device 20 may also invoke the spatio-temporalinterpolation unit 50. The spatio-temporal interpolation unit 50 mayperform spatio-temporal interpolation with respect to the reorderedtransformed HOA coefficients 33′/35′ to obtain the interpolatedforeground signals 49′ (which may also be referred to as the“interpolated nFG signals 49′”) and the remaining foreground directionalinformation 53 (which may also be referred to as the “V[k] vectors 53”)(116). The audio encoding device 20 may then invoke the coefficientreduction unit 46. The coefficient reduction unit 46 may performcoefficient reduction with respect to the remaining foreground V[k]vectors 53 based on the background channel information 43 to obtainreduced foreground directional information 55 (which may also bereferred to as the reduced foreground V[k] vectors 55) (118).

The audio encoding device 20 may then invoke the quantization unit 52 tocompress, in the manner described above, the reduced foreground V[k]vectors 55 and generate coded foreground V[k] vectors 57 (120).

The audio encoding device 20 may also invoke the psychoacoustic audiocoder unit 40. The psychoacoustic audio coder unit 40 may psychoacousticcode each vector of the energy compensated ambient HOA coefficients 47′and the interpolated nFG signals 49′ to generate encoded ambient HOAcoefficients 59 and encoded nFG signals 61. The audio encoding devicemay then invoke the bitstream generation unit 42. The bitstreamgeneration unit 42 may generate the audio bitstream 21 based on thecoded foreground directional information 57, the coded ambient HOAcoefficients 59, the coded nFG signals 61 and the background channelinformation 43.

FIG. 6 is a flowchart illustrating exemplary operation of an audiodecoding device, such as the audio decoding device 24 shown in FIG. 4,in performing various aspects of the techniques described in thisdisclosure. Initially, the audio decoding device 24 may receive theaudio bitstream 21 (130). Upon receiving the bitstream, the audiodecoding device 24 may invoke the extraction unit 72. Assuming forpurposes of discussion that the audio bitstream 21 indicates thatvector-based reconstruction is to be performed, the extraction unit 72may parse the bitstream to retrieve the above noted information, passingthe information to the vector-based reconstruction unit 92.

In other words, the extraction unit 72 may extract the coded foregrounddirectional information 57 (which, again, may also be referred to as thecoded foreground V[k] vectors 57), the coded ambient HOA coefficients 59and the coded foreground signals (which may also be referred to as thecoded foreground nFG signals 59 or the coded foreground audio objects59) from the audio bitstream 21 in the manner described above (132).

The audio decoding device 24 may further invoke the dequantization unit74. The dequantization unit 74 may entropy decode and dequantize thecoded foreground directional information 57 to obtain reduced foregrounddirectional information 55 _(k) (136). The audio decoding device 24 mayalso invoke the psychoacoustic decoding unit 80. The psychoacousticdecoding unit 80 may decode the encoded ambient HOA coefficients 59 andthe encoded foreground signals 61 to obtain energy compensated ambientHOA coefficients 47′ and the interpolated foreground signals 49′ (138).The psychoacoustic decoding unit 80 may pass the energy compensatedambient HOA coefficients 47′ to the fade unit 770 and the nFG signals49′ to the foreground formulation unit 78.

The audio decoding device 24 may next invoke the spatio-temporalinterpolation unit 76. The spatio-temporal interpolation unit 76 mayreceive the reordered foreground directional information 55 _(k)′ andperform the spatio-temporal interpolation with respect to the reducedforeground directional information 55 _(k)/55 _(k-1) to generate theinterpolated foreground directional information 55 _(k)″ (140). Thespatio-temporal interpolation unit 76 may forward the interpolatedforeground V[k] vectors 55 _(k)″ to the fade unit 770.

The audio decoding device 24 may invoke the fade unit 770. The fade unit770 may receive or otherwise obtain syntax elements (e.g., from theextraction unit 72) indicative of when the energy compensated ambientHOA coefficients 47′ are in transition (e.g., the AmbCoeftTransitionsyntax element). The fade unit 770 may, based on the transition syntaxelements and the maintained transition state information, fade-in orfade-out the energy compensated ambient HOA coefficients 47′ outputtingadjusted ambient HOA coefficients 47″ to the HOA coefficient formulationunit 82. The fade unit 770 may also, based on the syntax elements andthe maintained transition state information, and fade-out or fade-in thecorresponding one or more elements of the interpolated foreground V[k]vectors 55 _(k)″ outputting the adjusted foreground V[k] vectors 55_(k)′″ to the foreground formulation unit 78 (142).

The audio decoding device 24 may invoke the foreground formulation unit78. The foreground formulation unit 78 may perform matrix multiplicationthe nFG signals 49′ by the adjusted foreground directional information55 _(k)′″ to obtain the foreground HOA coefficients 65 (144). The audiodecoding device 24 may also invoke the HOA coefficient formulation unit82. The HOA coefficient formulation unit 82 may add the foreground HOAcoefficients 65 to adjusted ambient HOA coefficients 47″ so as to obtainthe HOA coefficients 11′ (146).

According to the techniques of this disclosure, audio decoding device 24may compute an HOA effect matrix based on the production screen size andreproduction window size. The HOA effect matrix may then be multipliedwith a given HOA rendering matrix R to create the screen-related HOArendering matrix. In some implementations, the adaptation of the HOArendering matrix may be done offline during, for example, aninitialization phase of audio decoding device 24, such that run-timecomplexity does not increase.

One proposed technique of this disclosure uses nine-hundred (900)equally spaced sampling point on a sphere (Ω⁹⁰⁰) each of the samplingpoints defined with direction (θ, φ) as described in Annex F.9 ofISO/IEC DIS 23008-3, Information technology—High efficiency coding andmedia delivery in heterogeneous environments—Part 3: 3D audio(hereinafter “DIS 23008”). Based on those directions, the audio decodingdevice 24 may compute a mode matrix Ψ⁹⁰⁰ as outlined in Annex F.1.5 ofDIS 23008. The audio decoding device 24 may modify the directions ofthose 900 sampling points via the mapping function, and audio decodingdevice 24 may compute the modified mode matrix Ψ_(m) ⁹⁰⁰ accordingly. Toavoid a mismatch between screen-related audio objects and screen-relatedHOA content, the audio decoding device 24 may use the same mappingfunctions already described in Clause 18.3 of DIS 23008. The audiodecoding device 24 may compute the effect matrix F is then computed as:

F=pinv(Ψ⁹⁰⁰ ^(T) )Ψ_(m) ⁹⁰⁰ ^(T)   (1)

The audio decoding device 24 may then compute the screen-relatedrendering matrix computed as:

D=RF   (2)

In some examples, the audio decoding device 24 may pre-compute and storethe matrix pinv (Ψ⁹⁰⁰ ^(T) ) to avoid repetition of one or more of theprocessing steps described above. The total number of remainingoperations in equation (1) and (2) to generate D is (900+M)*(N+1)⁴. Fora rendering matrix with the order N=4 and M=22 speakers, the complexityis approximately 0.58 weighted MOPS. According to another proposedtechnique of this disclosure, the audio decoding device 24 may use apreliminary effect matrix and loudness compensation to generate ascreen-related rendering matrix. When compared to using 900 equallyspaced sampling points in the manner described above, using thepreliminary effect matrix and loudness compensation may reduceprocessing complexity at the audio decoding device 24, while stillachieving desirable quality. By computing an effect matrix withoutaccounting for the rendering matrix, the audio decoding device 24 mayincrease computational complexity significantly, while providing littleor no benefit in terms of sound quality for some speaker configurations,such as 5.1 or 7.1 speaker configurations, which tend to have allspeakers located in the same plane. Additionally, by replacing certainHOA domain computations with loudspeaker domain computations, the audiodecoding device 24 may reduce the overall computational complexity, asHOA domain computations tend to be relatively complex compared toloudspeaker domain computations.

The audio decoding device 24 may compute the mapping based on Mequidistant spatial directions

−M>(N+1)², where N is the HOA order.

The audio decoding device 24 may compute the preliminary effect matrix{tilde over (F)}, which is in the loudspeaker feed domain from the HOAcoefficients associated with these directions rendered with the originalrendering matrix R as follows:

{tilde over (F)}=(Ψ^(M) R ¹)†(Ψ_(m) ^(M) R ¹).

In another example in accordance with aspects of this disclosure, theaudio decoding device 24 may compute the preliminary effect matrix{tilde over (F)}, which is in the loudspeaker feed domain, from the HOAcoefficients associated with these directions rendered with the originalrendering matrix R as follows:

{tilde over (F)}=(Ψ^((O,M)) ^(T) R ^(T))̂†Ψ^((O,M)) ^(T) R ^(T)).

where Ψ^((O,M)):=[S₁ ⁰ S₂ ⁰ . . . S_(M) ⁰]∈

^(O×M) as described in DIS, Annex F.1.5

In other examples in accordance with aspects of this disclosure, theaudio decoding device 24 may compute the preliminary effect matrix{tilde over (F)} without using the rendering matrix R. According tothese examples, the audio decoding device 24 may compute the preliminaryeffect matrix F which is in the HOA domain, from the HOA coefficientsassociated with these directions rendered with the original renderingmatrix R as follows:

{tilde over (F)}=(Ψ^((O,M)) ^(T) )̂†Ψ^((O,M)) ^(T) ).

where Ψ^((O,M)):=[S₁ ⁰ S₂ ⁰ . . . S_(M) ⁰]∈

^(O×M) as described in DIS, Annex F.1.5

According to some examples in accordance with this disclosure, the audiodecoding device 24 may apply loudness compensation for each spatialdirection l for the final matrix F, which is in the loudspeaker feeddomain, as follows:

${A(l)} = \sqrt{\frac{{\Sigma \left( {{\Psi_{m}^{M}(l)}R^{\prime}} \right)}2}{{\Sigma \left( {{\Psi^{M}(l)}R^{\prime}\overset{\sim}{F}} \right)}2}}$F = (Ψ^(M)R^(′))^(⋀)†diag(A)  (Ψ_(m)^(M)R^(′)).

In examples in accordance with aspects of this disclosure, the audiodecoding device 24 may apply loudness compensation for each spatialdirection l for the final matrix F, which is in the loudspeaker feeddomain, as follows:

${A(l)} = \sqrt{\frac{\left( {RS}_{ml}^{O} \right)^{T}\left( {RS}_{ml}^{O} \right)}{\left( {\overset{\sim}{F}{RS}_{l}^{O}} \right)^{T}\left( {\overset{\sim}{F}{RS}_{l}^{O}} \right)}}$F = (Ψ^((O, M)^(T))R^(T))^(⋀)†diag(A)  (Ψ_(m)^((O, M)^(T))R^(T)).

In other examples of this disclosure in which the preliminary effectmatrix {tilde over (F)} (e.g., in the HOA domain) is computed withoutusing the rendering matrix R, the audio decoding device 24 may applyloudness compensation for each spatial direction l for the final matrixF (e.g., in the HOA domain) as follows:

${A(l)} = \sqrt{\frac{\left( {RS}_{ml}^{O} \right)^{T}\left( {RS}_{ml}^{O} \right)}{\left( {R\overset{\sim}{F}S_{l}^{O}} \right)^{T}\left( {R\overset{\sim}{F}S_{l}^{O}} \right)}}$F = (Ψ^((O, M)^(T)))^(⋀)†diag(A)  (Ψ_(m)^((O, M)^(T))).

In some examples, the audio decoding device 24 may implement thetechniques of this disclosure to dynamically generate a mode matrixΨ^((O,M)) to accommodate perspective changes affecting the correspondingvideo data. It will be appreciated that the audio decoding device 24 mayimplement the techniques to manipulate the mode matrix Ψ^((O,M)) basedon any one or more of a variety of perspective parameters discussedherein. By way of example, the dynamic perspective-based updating of themode matrix Ψ^((O,M)) is described below with respect to zoominginformation of the video data. During a dynamic zooming event, the audiodecoding device 24 may compute a new effect matrix F using thedynamically-updated mode matrix Ψ^((O,M)). Upon detecting an end to thedynamic zooming event (e.g., detecting that the zooming status is nowstatic), the audio decoding device 24 may revert to the mode matrixΨ_(m) ⁹⁰⁰ where the number of spatial sampling points used (‘M’) is 900.As described in further detail below, the audio decoding device 24 mayimplement the screen-based adaptation techniques of this disclosure toaccommodate dynamic zooming events while conserving computing resourceusage.

An example of the screen-based adaption techniques of this disclosurethat the audio decoding device 24 may implement to accommodate dynamiczoom events may be performed (e.g., by various combinations of thecomponents of the audio decoding device 24) using the steps outlinedbelow. First, the audio decoding device 24 may generate a mode matrixΨ^((O,M)) as outlined in Annex F.1.5 of DIS 23008. If the audio decodingdevice 24 detects that the perspective of the corresponding videocontent is static (e.g., no zoom event is occurring currently), then theaudio decoding device 24 may set the value of ‘M’ to be 900 (ninehundred). In other words, in the case of a static perspective, the audiodecoding device 24 may generate the mode matrix Ψ^((O,M)) using a totalof 900 sampling points. However, if the audio decoding device 24 detectsthat the video data is currently undergoing a zooming event (either azoom-in or a zoom-out), then the audio decoding device 24 maydynamically generate the number of sample points.

According to some aspects of this disclosure, during an ongoing zoomingevent, the audio decoding device 24 may compute the mode matrixΨ^((O,M)) using the HOA order of the audio data as a computationalparameter. For instance, the audio decoding device 24 may compute thenumber of sampling points according to the formula:

M=(N+2)²

In this example, ‘M’ denotes the number of sampling points, and ‘N’denotes the order of the ambitions coefficients. Thus, according tothese examples of the dynamic zoom accommodation in screen-basedadaptation, the audio decoding device 24 would use 36 sampling points togenerate the mode matrix if the highest order coefficients are of thefourth (4the) order. More specifically, in this particular example,‘N’=4, yielding a value of 36 for ‘M’ when solving the above equation.Applying this equation to other use case scenarios, the audio decodingdevice 24 would use 49 sampling points to generate the mode matrix ifthe highest order coefficients are of the fifth (5the) order, or theaudio decoding device 24 would use 64 sampling points to generate themode matrix if the highest order coefficients are of the sixth (6the)order. As defined in Annex F.9 of DIS 23008, the directions of the ‘M’sampling points are given by (θ, φ).

Second, the audio decoding device 24 may modify the directions of the Msampling points, using the mapping function defined in Clause 18.3 ofDIS 23008. Based on the computation of ‘M’ and the modified directions,the audio decoding device 24 may compute the mode matrix Ψ^((O,M)). Asdescribed above, the mode matrix Ψ^((O,M)):=[S₁ ⁰ S₂ ⁰. . . S_(M) ⁰]∈

^(O×M) according to Annex F.1.5 of DIS 23008.

Third, the audio decoding device 24 may compute or generate apreliminary effects matrix {tilde over (F)} (e.g., in the HOA domain) asfollows:

{tilde over (F)}=Ψ_(m) ^((O,M))Ψ^((O,M)) ^(†)

where Ψ^((O,M)) ^(†) denotes the pseudo-inverse of the mode matrix Ψ_(m)^((O,M)).

Fourth, the audio decoding device 24 may compute a loudness value byusing the HOA rendering matrix R for each spatial direction. Morespecifically, according to the example workflow described herein, theaudio decoding device 24 may use the HOA rendering matrix R as definedin clause 12.4.3.2 of DIS. The spatial directions are denoted herein asl=1. . . M. For instance, the audio decoding device 24 may compute theloudness correction value according to the following formula:

${A(l)} = \sqrt{\frac{\left( {RS}_{m,l}^{O} \right)^{T}\left( {RS}_{m,l}^{O} \right)}{\left( {R\overset{\sim}{F}S_{l}^{O}} \right)^{T}\left( {R\overset{\sim}{F}S_{l}^{O}} \right)}}$

Fifth, the audio decoding device 24 may compute the final effect matrixusing the mode matrix computed as described above. For instance, theaudio decoding device 24 may compute the final effect matrix F, which inthe HOA domain, according to the following formula:

F=Ψ_(m) ^((O,M))diag(A)Ψ^((O,M)) ^(†)

where diag (A) denotes a diagonal matrix including the vector A.

Sixth, the audio decoding device 24 may compute the new renderingmatrix, according to the formula D=RF. According to the zoom-dependentadaptation techniques of this disclosure, if no local zoom informationis available to the audio decoding device 24, then the audio decodingdevice 24 may not apply any zooming-based adaption to the generation ofthe mode matrix Ψ^((O,M)) or, as a result, the final effect matrix{tilde over (F)}. Thus, according to the dynamic zoom accommodationtechniques of this disclosure, the audio decoding device 24 may applythe same algorithmic principles as described for the screen-relatedprocessing for Higher Order Ambitions, but the audio decoding device 24may adapt the rendering matrix at runtime according to the data providedby the LocalZoomAreaSize( )interface. Upon detecting that that thedynamic zooming event has concluded (e.g., the perspective of the screencontent is now static), the audio decoding device 24 may revert to usinga value of 900 for ‘M’. In other words, the audio decoding device 24 mayrevert to using 900 sampling points in generating the mode matrix.

During a dynamic zooming event, the audio decoding device 24 may computethe new effect matrix F based on a mode matrix Ψ^((O,M)) with M=(N+2)²equally-spaced sampling points for which directions are given in AnnexF.2 to F.9 of DIS. Once the audio decoding device 24 detects that thezoom is stationary, the audio decoding device 24 may compute the neweffect matrix F based on a mode matrix Ψ^((O,M)) with M=900 spatialsampling points as decribed above. While zoom events are describedherein with pinch or pinch-out gestures supplied by way of an inputdevice (e.g., mouse and/or keyboard) or an input/output device (e.g., atouchscreen or capacitive stylus-operated screen), it will beappreciated that zoom events may be triggered in response to otherstimuli (e.g., other types of user input) as well.

The dynamic zoom adjustment of this disclosure may provide one or morepotential advantages and improvements over existing techniques. Forinstance, by reducing the number of sampling points used in computingthe mode matrix during a dynamic zoom event, the audio decoding device24 may implement the techniques of this disclosure to reduce thecomputational complexity and resource expenditure in addressingscreen-based adaptation during rendering of audio feeds. As describedabove, in some scenarios, the audio decoding device 24 may reduce thesampling points from 900 to 36 during the zoom event. By reducing thecomputational complexity during mode matrix computation, the audiodecoding device 24 may implement the techniques of this disclosure tomore efficiently perform screen-based adaptation, while delivering audiofeeds of reduced quality only during the zoom event. In turn, the audiodecoding device 24 may restore the audio feed quality once the zoom iscomplete.

In some examples, the audio decoding device 24 may perform thescreen-related adaptation techniques of this disclosure only if aparticular syntax element is enabled. For instance, in these examples,the audio decoding device 24 may perform screen-related adaption of themode matrix only if the isScreenRelative flag in the HOAConfig( )sectionof Table 119 of DIS is signaled in an enabled state (e.g., set to avalue of 1). Said another way, in these examples, the audio decodingdevice 24 may perform screen-related adaption of the mode matrix only ifthe audio decoding device 24 receives, in a bitstream, theisScreenRelative flag in an enabled state (e.g., set to the value of 1).

Additionally, in accordance with one or more aspects of this disclosure,the audio decoding device 24 may only compute the HOA rendering matrixduring the initialization phase. For instance, the audio decoding device24 may limit the HOA rendering matrix computation to the initializationphase because the screen-related adaptation techniques of thisdisclosure modify the HOA rendering matrix that is used for a soundfield. If no local screen size information is available to the audiodecoding device 24, then the audio decoding device 24 may not apply anyscreen-related adaptation. In some examples, in instances where theaudio decoding device 24 only has access to the azimuth screen sizeinformation, the audio decoding device 24 may not apply anyscreen-related adaptation in the vertical dimension.

By performing loudness compensation, the audio decoding device 24 may,for example, compensate for the effects of mapping. In the exampleabove, 1 is a spatial direction from 1 to capital M, and A(1) is avector with A1 to Am entries. “diag(A)” represents a matrix withdiagonal entries corresponding to A(1), and other locations in thematrix equal to 0. The above described techniques include a loudnesscompensation step that the audio decoding device 24 may use to equalizethe undesired direction-dependent loudness differences caused by thespatial stretching and/or squeezing of the effect matrix. Thepreliminary effect matrix and the resulting effect matrix F are in theloudspeaker signal domain.

The audio decoding device 24 may then compute the screen-relatedrendering matrix as:

D=FR.

A first example of the screen-based adaptation techniques of thisdisclosure will now be described with references to FIGS. 7-11. FIG. 7Ashows an example of a mapping function that may be used map an azimuthangle for a reference screen to an azimuth angle for a viewing window.FIG. 7B shows an example of mapping function that may be used map anelevation angle for a reference screen to an elevation angle for aviewing window. In the example of FIGS. 7A and 7B, the angles of thereference screen are 29 to −29 degrees azimuth and 16.3 to −16.3 degreeselevation, and the angles of the viewing window are 58 to −58 degreesazimuth and 32.6 to −32.6 degrees elevation. Thus, in the example ofFIGS. 7A and 7B, the viewing window is twice as large as referencescreen.

As used in this disclosure, a viewing window may refer to all or part ofa screen used for reproducing video. A television that can be used inaccordance with the aspects of this disclosure may, in various examples,represent an integrated device, such as a device that includes one ormore speakers and/or a display. In various examples, the television maybe a so-called “smart” television or smart TV, in that the televisioncan process audiovisual bitstreams received over wired and/or wireless(e.g., Ethernet® or WiFi®) connections. A smart television or “smart TV”may include a communication interface (e.g., an Ethernet® card or WiFi®card), along with memory device(s) and one or more processors. Whenplaying back a movie in a full screen mode on a television, tablet,phone or other such device, the viewing window may correspond to theentire screen of the device. In other examples, however, a viewingwindow may correspond to less than the entire screen of the device. Forexample, a device playing back four sporting events simultaneously mayinclude four distinct viewing windows on one screen, or a device mayhave a single viewing window for playing back video and use theremaining screen area for displaying other content. The field of view ofa viewing window may be determined based on such parameters as aphysical size of the viewing window and/or a distance (either measuredor assumed) from the viewing window to a viewing location. The field ofview may, for example, be described by azimuth angles and elevationangles.

As used in this disclosure, a reference screen refers to a field of viewcorresponding to the sound field of HOA audio data. For example, HOAaudio data may be generated or captured with respect to a certain fieldof view (i.e. a reference screen) but may be reproduced with respect toa different field of view (e.g. the field of view of a viewing window).As explained in this disclosure, the reference screen provides areference by which an audio decoder may adapt the HOA audio data forlocal playback on a screen that differs in size, location, or some othersuch characteristic from the reference screen. For purposes ofexplanation, certain techniques in this disclosure may be described withreference to a production screen and reproduction screen. It should beunderstood that these same techniques are applicable to referencescreens and viewing windows.

FIG. 8 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow for the first example. In FIG. 8, the dots correspond to amapping destination, while the lines going into the dots correspondmapping trails. The dashed-lined rectangle corresponds to a referencescreen size, and the solid-lined rectangle corresponds to a viewingwindow size.

FIG. 9 shows an example of how the screen-related effect may cause anincrease of the HOA order of the content. In the example of FIG. 9, theeffect matrix is computed to create 49 HOA coefficients (6^(the) order)from a 3^(rd) order input material. However, satisfactory results mayalso be achieved if the matrix is computed as square matrix with(N+1)²×(N+1)² elements.

FIG. 10 shows an example of how the effect matrix may be pre-renderedand applied to the loudspeaker rendering matrix, thus requiring no extracomputation at runtime.

FIG. 11 shows an example of how if the effect matrix may result in ahigher order content (e.g., 6^(the) order), a rendering matrix in thisorder may be multiplied to pre-compute the final rendering matrix in theoriginal order (here 3^(rd) order).

A second example of the screen-based adaptation techniques of thisdisclosure will now be described with references to FIGS. 12-13. FIG.12A shows an example of a mapping function that may be used map anazimuth angle for a reference screen to an azimuth angle for a viewingwindow. FIG. 12B shows an example of mapping function that may be usedmap an elevation angle for a reference screen to an elevation angle fora viewing window. In the example of FIGS. 12A and 12B, the angles of thereference screen are 29 to −29 degrees azimuth and 16.3 to −16.3 degreeselevation, and the angles of the viewing window are 29 to −29 degreesazimuth and 32.6 to −32.6 degrees elevation. Thus, in the example ofFIGS. 12A and 12B, the viewing window is twice as tall but with the samewidth as the reference screen. FIG. 12C shows a computed HOA effectmatrix for the second example.

FIG. 13 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow for the second example. In FIG. 13, the dots correspond to amapping destination, while the lines going into the dots correspondmapping trails. The dashed-lined rectangle corresponds to a referencescreen size, and the solid-lined rectangle corresponds to a viewingwindow size.

A third example of the screen-based adaptation techniques of thisdisclosure will now be described with references to FIGS. 14-15. FIG.14A shows an example of a mapping function that may be used to map anazimuth angle for a reference screen to an azimuth angle for a viewingwindow. FIG. 14B shows an example of mapping function that may be usedmap an elevation angle for a reference screen to an elevation angle fora viewing window. In the example of FIGS. 14A and 14B, the angles of thereference screen are 29 to −29 degrees azimuth and 16.3 to −16.3 degreeselevation, and the angles of the viewing window are 58 to −58 degreesazimuth and 16.3 to −16.3 degrees elevation. Thus, in the example ofFIGS. 14A and 14B, the viewing window is twice as wide as the referencescreen but with the same height as the reference screen. FIG. 14C showsa computed HOA effect matrix for the third example.

FIG. 15 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow for the third example. In FIG. 15, the dots correspond to amapping destination, while the lines going into the dots correspondmapping trails. The dashed-lined rectangle corresponds to a referencescreen size, and the solid-lined rectangle corresponds to a viewingwindow size.

A fourth example of the screen-based adaptation techniques of thisdisclosure will now be described with references to FIGS. 16-17. FIG.16A shows an example of a mapping function that may be used map anazimuth angle for a reference screen to an azimuth angle for a viewingwindow. FIG. 16B shows an example of mapping function that may be usedmap an elevation angle for a reference screen to an elevation angle fora viewing window. In the example of FIGS. 16A and 16B, the angles of thereference screen are 29 to −29 degrees azimuth and 16.3 to −16.3 degreeselevation, and the angles of the viewing window are 49 to −9 degreesazimuth and 16.3 to −16.3 degrees elevation. Thus, in the example ofFIGS. 14A and 14B, the viewing window is twice as wide as the referencescreen but with the same height as the reference screen. FIG. 16C showsa computed HOA effect matrix for the third example.

FIG. 17 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow for the fourth example. In FIG. 17, the dots correspond to amapping destination, while the lines going into the dots correspondmapping trails. The dashed-lined rectangle corresponds to a referencescreen size, and the solid-lined rectangle corresponds to a viewingwindow size.

A fifth example of the screen-based adaptation techniques of thisdisclosure will now be described with references to FIGS. 18-19. FIG.18A shows an example of a mapping function that may be used map anazimuth angle for a reference screen to an azimuth angle for a viewingwindow. FIG. 18B shows an example of mapping function that may be usedmap an elevation angle for a reference screen to an elevation angle fora viewing window. In the example of FIGS. 18A and 18B, the angles of thereference screen are 29 to −29 degrees azimuth and 16.3 to −16.3 degreeselevation, and the angles of the viewing window are 49 to −9 degreesazimuth and 16.3 to −16.3 degrees elevation. Thus, in the example ofFIGS. 18A and 18B, the viewing window is shifted in the azimuth locationrelative to the reference screen. FIG. 18C shows a computed HOA effectmatrix for the fifth example.

FIG. 19 shows a vector field for a desired screen-related expansioneffect of the sound field as an effect of reference screen and viewingwindow for the fourth example. In FIG. 19, the dots correspond to amapping destination, while the lines going into the dots correspondmapping trails. The dashed-lined rectangle corresponds to a referencescreen size, and the solid-lined rectangle corresponds to a viewingwindow size.

FIGS. 20A-20F are block diagrams illustrating another example of anaudio decoding device 900 that may implement various aspects of thetechniques for screen-based adaptation of audio described in thisdisclosure. For simplicity, not all aspects of audio decoding device 900are shown in FIGS. 20A-20F. It is contemplated that the features andfunctions of audio decoding device 900 may be implemented in conjunctionwith the features and functions of other audio decoding devicesdescribed in this disclosure, such as audio decoding device 24 describedabove with respect to FIGS. 2 and 4.

Audio decoding device 900 includes USAC decoder 902, HOA decoder 904,local rendering matrix generator 906, signaled/local rendering matrixdecider 908, and loudspeaker renderer 910. Audio decoding device 900receives an encoded bitstream (e.g. an MPEG-H 3D audio bitstream). USACdecoder 902 and HOA decoder 904 decode the bitstream using the USAC andHOA audio decoding techniques described above. Local rendering matrixgenerator 906 generates one or more rendering matrices based at least inpart on the local loudspeaker configuration of the system which will beplaying back the decoded audio. The bitstream may also include one ormore rendering matrices which may be decoded from the encoded bitstream.Local/Signaled Rendering matrix decider 908 determines which of thelocally generated or signaled rendering matrices to use when playingback the audio data. Loudspeaker renderer 910 outputs audio to one ormore speakers based on the chosen rendering matrix.

FIG. 20B is a block diagram illustrating another example of audiodecoding device 900. In the example of FIG. 20B, audio decoding device900 further includes effect matrix generator 912. Effect matrixgenerator 912 may determine from the bitstream a reference screen sizeand determine, based on the system being used to display correspondingvideo data, a viewing window size. Based on the reference screen sizeand the viewing window size, effect matrix generator 912 may generate aneffect matrix (F) for modifying the rendering matrix (R′) selected bylocal/signaled rendering matrix decider 908. In the example of FIG. 20B,loudspeaker renderer 910 may output audio to the one or more speakersbased on the modified rendering matrix (D). In the example, of FIG. 20C,audio decoding device 900 may be configured to only render the effect ifin HOADecoderConfig( )the flag isScreenRelative flag ==1.

According to the techniques of this disclosure effect matrix generator912 may also generate an effect matrix in response to screen rotation.Effect matrix generator 912 may, for example, generate an effect matrixaccording to the following algorithm. An example algorithm for the newmapping function, in pseudocode, is:

-   -   %1. compute relative screen mapping parameter    -   originalWidth=originalAngles.azi(1)-originalAngles.azi(2);    -   original Height=original Angles.ele(1)-originalAngles.ele(2):,    -   newWidth=newAngles.azi(1)-newAngles.azi (2);    -   newHeight=newAngles.ele(1)-newAngles.ele(2):    -   %2. find center of reference screen and center of viewing        window.    -   originalCenter.azi=originalAngles.azi(1)-originalWidth*0.5;    -   originalCenter.ele=originalAngles.ele(1)-originalHeight*0.5;    -   newCenter.azi=newAngles.azi(1)-newWidth*0.5;    -   newCenter.ele=newAngles.ele(1)-newHeight*0.5;    -   %3. do relative screen related mapping    -   heightRatio=newHeight/originalHeight;    -   widthRatio=newWidth/originalWidth;    -   Mapping of equally distributed spatial positions using MPEG-H        screen related mapping function using heightRatio and        widthRatio, rather than the absolute positions of production and        viewing window.    -   %4. rotate soundfield    -   rotating the spatial position processed in (3.) from        originalCenter to newCenter.    -   %5. computing HOA effect matrix    -   using original spatial positions and processed spatial positions        (from 4.)

According to the techniques of this disclosure effect matrix generator912 may also generate an effect matrix in response to screen rotation.Effect matrix generator 912 may, for example, generate an effect matrixaccording to the following algorithm.

-   -   1. Compute relative screen mapping parameter:        -   widthRatio=localWidth/productionWidth;        -   heightRatio=localHeight/productionHeight;    -   with:        -   productionWidth=production_Azi_L-production_Azi_R;        -   productionHeight=production_Ele_Top-production_Ele_Down;        -   local Width=local_Azi_L-local_Azi_R;        -   localHeight=local_Ele_Top-local_Ele_Down;    -   2. Compute center coordinates of normative production screen and        center of local reproduction screen:        -   productionCenter_Azi=production_Azi_L-productioWidth/2;        -   productionCenter_Ele=production_Ele_Top-productionHeight/2;        -   localCenter_Azi=local _Azi_L-localWidth/2;        -   localCenter_Ele=local_Ele_Top-localHeight/2;    -   Screen-related mapping:        -   Mapping of Ω⁹⁰⁰ with screen-related mapping function using            heightRatio and widthRatio to Ω_(m) ⁹⁰⁰.    -   4. Rotate positions:        -   Rotating the spatial position Ω_(M) ⁹⁰⁰ from            productionCenter coordinate to localCenter coordinate, using            rotation kernel R, resulting in Ω_(mr) ⁹⁰⁰

$\begin{matrix}{{R\left( {\theta,\varphi} \right)} = {{{\begin{bmatrix}{\cos \; \theta} & 0 & {\sin \; \theta} \\0 & 1 & 0 \\{{- \sin}\; \theta} & 0 & {\cos \; \theta}\end{bmatrix}\begin{bmatrix}{\cos \; \varphi} & {{- \sin}\; \varphi} & 0 \\{\sin \; \varphi} & {\cos \; \varphi} & 0 \\0 & 0 & 1\end{bmatrix}}.y}\text{-}{axis}\mspace{14mu} {rotation}\mspace{14mu} ({pitch})\mspace{14mu} z\text{-}{axis}\mspace{14mu} {rotation}\mspace{14mu} ({yaw})}} & (3)\end{matrix}$

-   -   5. Computing HOA effect matrix:

F=pinv(Ψ⁹⁰⁰ ^(T) )Ψ_(mr) ⁹⁰⁰ ^(T) .   (4)

with Ψ_(mr) ⁹⁰⁰ being the mode matrix created from Ω_(mr) ⁹⁰⁰.

FIG. 20C is a block diagram illustrating another example of audiodecoding device 900. In the example of FIG. 20C, audio decoding device900 generally operates in the same manner described above for theexample of FIG. 20B, but in the example of FIG. 20C, effect matrixgenerator 912 is further configured to determine a scaling factor for azoom operation, and based on the scaling information, the referencescreen size, and the viewing window size, generate an effect matrix (F)for modifying the rendering matrix (R′) selected by local/signaledrendering matrix decider 908. In the example of FIG. 20C, loudspeakerrenderer 910 may output audio to the one or more speakers based on themodified rendering matrix (D). In the example, of FIG. 20C, audiodecoding device 900 may be configured to only render the effect if inHOADecoderConfig( )the flag isScreenRelativeHOA flag==1.

The flag isScreenRelativeHOA in the HOADecoderConfig( ) syntax table(shown below as Table 1) is sufficient to enable the adaptation ofscreen-related HOA content to the reproduction window size (which mayalso be referred to as a “reproduction screen size”). Information on thenominal production screen may be signaled separately as part of ametadata audio element.

TABLE 1 Syntax of HOADecoderConfig( ), Table 120 in DIS 23008 No. ofSyntax bits Mnemonic HOADecoderConfig(numHOATransportChannels) { MinAmbHoaOrder = escapedValue(3,5,0) − 1; 3, 8 uimsbf isScreenRelativeHOA; 1 uimsbf  MaxNoOfDirSigsForPrediction = 2 uimsbfMaxNoOfDirSigsForPrediction + 1;  NoOfBitsPerScalefactor = 4 uimsbf NoOfBitsPerScalefactor + 1;  CodedSpatialInterpolationTime; 3 uimsbf SpatialInterpolationMethod; 1 bslbf  CodedVVecLength; 2 uimsbf MaxGainCorrAmpExp; 3 uimsbf  } } NOTE: MinAmbHoaOrder = 30 . . . 37 arereserved.

FIG. 20D is a block diagram illustrating another example of audiodecoding device 900. In the example of FIG. 20D, audio decoding device900 further includes loudness compensator 914, final effect matrixgenerator 916, and final renderer generator 918. Loudness compensator914 performs loudness compensation as described above. Loudnesscompensator 914, for example, performs loudness compensation for eachspatial direction l applied for the final matrix F, as described above.Final Effect Matrix generator 916 generates the final effect matrix asdescribed above. Final renderer generator 918 creates the finalrendering matrix, for example, by performing the D=FRY computationdescribed above.

FIG. 20E is a block diagram illustrating another example of audiodecoding device 900. In the example of FIG. 20E, the preliminary effectmatrix and effect matrix generator 912 may not use the originalrendering matrix R as an input in generating the preliminary effectmatrix F.

FIG. 20F is a block diagram illustrating another example of audiodecoding device 900. In the example of FIG. 20F, the preliminary effectmatrix and effect matrix generator 912 may use a local zoom size as anadditional parameter in generating the mode matrix. In some examples,the preliminary effect matrix and effect matrix generator 912 use thelocal zoom size of a zoomed window (e.g., a window that is zoomed-in orzoomed-out in comparison to a reference window) as a parameter ingenerating the mode matrix. For instance, the preliminary effect matrixand effect matrix generator 912 may detect a user-initiated zoomcommand, such as by processing data received from other components ofthe audio decoding device 24. In turn, the preliminary effect matrix andeffect matrix generator 912 may obtain FOV parameters (e.g., one or moreof modified azimuth and/or modified elevation angle information) basedon parameters of the particular zooming operation that exhibits zoomingcharacteristics provided by way of the user-initiated zoom command. Thepreliminary effect matrix and effect matrix generator 912 mayincorporate the FOV parameters corresponding to the zooming operation ingenerating the mode matrix. As such, FIG. 20F illustrates an exampleimplementation of the audio decoding device 900 that is configured toperform the dynamic zoom adaptation techniques described above.

An audio playback system of the present disclosure, such as audioplayback system 16, may be configured to generate a preliminary effectmatrix based on a rendering matrix and render the HOA audio signal basedon the preliminary effect matrix. Audio playback system 16 may, forexample, be configured to determine the rendering matrix based on aspeaker configuration. Audio playback system 16 may generate a finalrendering matrix based on the preliminary effect matrix and render theHOA audio signal based on the preliminary effect matrix. Audio playbacksystem 16 may, for example, generate the preliminary effect matrix basedon one or more field of view (FOV) parameters of a reference screen andone or more FOV parameters of a viewing window. To generate thepreliminary effect matrix, audio playback system 16 may be configured toperform a mapping of spatial directions in response to a screen relatedadaptation and compute the preliminary effect matrix based on HOAcoefficients associated with the spatial directions. In such examples,the preliminary effect matrix may be a locally generated preliminaryeffect matrix. Audio playback system 16 may be further configured tocompensate for loudness for a plurality of spatial directions based onthe rendering matrix.

An audio playback system of the present disclosure, such as audioplayback system 16, may additionally or alternatively be configured toperform a loudness compensation process as part of generating an effectmatrix and render the HOA audio signal based on the effect matrix. Toperform the loudness compensation process, audio playback system 16 maycompensate for loudness for a plurality of spatial directions based on arendering matrix. To perform the loudness compensation process, audioplayback system 16 may compensate for loudness for a plurality ofspatial directions based on a rendering matrix. To perform the loudnesscompensation process, audio playback system 16 may be configured tocompensate for loudness for a plurality of spatial directions based on amapping function. To perform the loudness compensation process, audioplayback system 16 may be configured to determine a minimum errorbetween a plurality of original sound locations and a plurality ofcorresponding mapped destinations (e.g. the mapping destinations inFIGS. 15-19). To perform the loudness compensation process, audioplayback system 16 may be configured to determine an energynormalization between a plurality of original sound locations and aplurality of corresponding mapped destinations.

An audio playback system of the present disclosure, such as audioplayback system 16, may be configured to render an HOA audio signal byrendering the HOA audio signal over one or more speakers (e.g. speakers3) based on one or more FOV parameters of a reference screen (e.g. FOVparameters 13′) and one or more FOV parameters of a viewing window. Therendering may, for example, be further based on a scaling factorobtained in response to a user initiated zoom operation. In someexamples, the one or more FOV parameters for the reference screen mayinclude a location of a center of the reference screen and a location ofa center of the viewing window.

Audio playback system 16 may, for example, receive a bitstream ofencoded audio data comprising the HOA audio signal. The encoded audiodata may be associated with corresponding video data. Audio playbacksystem 16 may obtain from the bitstream the one or more FOV parameters(e.g. FOV parameters 13′) of the reference screen for the correspondingvideo data.

Audio playback system 16 may also obtain the one or more FOV parametersof the viewing window for displaying the corresponding video data. TheFOV parameters of the viewing window may be determined locally based onany combination of user input, automated measurements, default values,or the like.

Audio playback system 16 may determine a renderer, from audio renderers22, for the encoded audio data, based on the one or more FOV parametersof the viewing window and the one or more FOV parameters of thereference screen, modify one of audio renderers 22, and based on themodified renderer and the encoded audio data, render the HOA audiosignal over the one or more speakers. Audio playback system 16 maymodify one of audio renderers 22 further based on the scaling factorwhen a zoom operation is performed.

Audio playback system 16 may, for example, determine the renderer forthe encoded audio data based on a speaker configuration, including butnot necessarily limited to a spatial geometry of one or more speakersand/or a number of speakers available for playback.

Audio renders 22 may, for example, include an algorithm for convertingthe encoded audio data to a reproduction format and/or utilize arendering format. The rendering format may, for example, include any ofa matrix, a ray, a line, or a vector. Audio renderers 22 may be signaledin the bitstream or determined based on a playback environment.

The one or more FOV parameters for the reference screen may include oneor more azimuth angles for the reference screen. The one or more azimuthangles for the reference screen may include a left azimuth angle for thereference screen and a right azimuth angle for the reference screen. Theone or more FOV parameters for the reference screen may alternatively oradditionally include one or more elevation angles for the referencescreen. The one or more elevation angles for the reference screen mayinclude an upper elevation angle for the reference screen and a lowerelevation angle for the reference screen.

The one or more FOV parameters for the viewing window may include one ormore azimuth angles for the viewing window. The one or more azimuthangles for the viewing window may include a left azimuth angle for theviewing window and a right azimuth angle for the viewing window. The oneor more FOV parameters for the viewing window may include one or moreazimuth angles for the viewing window. The one or more elevation anglesfor the viewing window may include an upper elevation angle for theviewing window and a lower elevation angle for the viewing window.

Audio playback system 16 may modify one or more of audio renderers 22 bydetermining an azimuth angle mapping function for modifying an azimuthangle of a speaker based on the one or more FOV parameters of thereference screen and the one or more FOV parameters of the viewingwindow and modifying an azimuth angle for a first speaker of the one ormore speakers to generate a modified azimuth angle for the first speakerbased on the azimuth angle mapping function.

The azimuth angle mapping function comprises:

$\phi^{\prime} = \left\{ \begin{matrix}{{\frac{\phi_{right}^{repro} + {180{^\circ}}}{\phi_{right}^{nominal} + {180{^\circ}}} \cdot \left( {\phi + {180{^\circ}}} \right)} - {180{^\circ}}} & {{{for}\mspace{14mu} - {180{^\circ}}} \leq \phi < \phi_{right}^{nominal}} \\{{\frac{\phi_{left}^{repro} - \phi_{right}^{repro}}{\phi_{left}^{nominal} - \phi_{right}^{nominal}} \cdot \left( {\phi - \phi_{right}^{nominal}} \right)} + \phi_{right}^{repro}} & {{{for}\mspace{14mu} \phi_{right}^{nominal}} \leq \phi < \phi_{left}^{nominal}} \\{{\frac{{180{^\circ}} - \phi_{left}^{repro}}{{180{^\circ}} - \phi_{left}^{nominal}} \cdot \left( {\phi - \phi_{left}^{nominal}} \right)} + \phi_{left}^{repro}} & {{{for}\mspace{14mu} \phi_{left}^{nominal}} \leq \phi < 180^{{^\circ}}}\end{matrix} \right.$

-   wherein φ′ represents the modified azimuth angle for the first    speaker;-   φ represents the azimuth angle for the first speaker;-   φ_(left) ^(nominal) represents a left azimuth angle of the reference    screen;-   φ_(right) ^(nominal) represents a right azimuth angle of the    reference screen;-   φ_(left) ^(repro) represents a left azimuth angle of the viewing    window; and,-   φ_(right) ^(repro) represents a right azimuth angle of the viewing    window.

Audio playback system 16 may modify the renderer by determining anelevation angle mapping function for modifying an elevation angle of aspeaker based on the one or more FOV parameters of the reference screenand the one or more FOV parameters of the viewing window and modifyingan elevation angle for a first speaker of the one or more speakers basedon the elevation angle mapping function.

The elevation angle mapping function comprises:

$\theta^{\prime} = \left\{ \begin{matrix}{{\frac{\theta_{bottom}^{repro} + {90{^\circ}}}{\theta_{bottom}^{nominal} + {90{^\circ}}} \cdot \left( {\theta + {90{^\circ}}} \right)} - {90{^\circ}}} & {{{for}\mspace{14mu} - {90{^\circ}}} \leq \theta < \theta_{bottom}^{nominal}} \\{{\frac{\theta_{top}^{repro} - \theta_{bottom}^{repro}}{\theta_{top}^{nominal} - \theta_{bottom}^{nominal}} \cdot \left( {\theta - \theta_{bottom}^{nominal}} \right)} + \theta_{bottom}^{repro}} & {{{for}\mspace{14mu} \theta_{bottom}^{nominal}} \leq \theta < \theta_{top}^{nominal}} \\{{\frac{{90{^\circ}} - \theta_{top}^{repro}}{{90{^\circ}} - \theta_{top}^{nominal}} \cdot \left( {\theta - \theta_{top}^{nominal}} \right)} + \theta_{top}^{repro}} & {{{for}\mspace{14mu} \theta_{top}^{nominal}} \leq \theta < 90^{{^\circ}}}\end{matrix} \right.$

-   wherein θ′ represents the modified elevation angle for the first    speaker;-   θ represents the elevation angle for the first speaker;-   θ_(top) ^(nominal) represents a top elevation angle of the reference    screen;-   θ_(bottom) ^(nominal) represents a bottom elevation angle of the    reference screen;-   θ_(top) ^(repro) represents a top elevation angle of the viewing    window; and,-   θ_(bottom) ^(repro) represents a bottom elevation angle of the    viewing window.

Audio playback system 16 may modify the renderer in response to a userinitiated zoom function at the viewing window. For example, in responseto a user initiated zoom function, Audio playback system 16 maydetermine one or more FOV parameters of a zoomed viewing window and,based on the one or more FOV parameters of the reference screen and theone or more FOV parameters of the zoomed viewing window, modify therenderer. Audio playback system 16 may also modify the renderer bydetermining one or more FOV parameters of a zoomed viewing window basedon the scaling factor and the one or more FOV parameters of the viewingwindow, determining an azimuth angle mapping function for modifying anangle, such as an azimuth angle of a speaker, based on the one or moreFOV parameters of the zoomed viewing window and the one or more FOVparameters of the reference screen, and modifying an angle (e.g., anazimuth angle) for a first speaker of the one or more speakers togenerate a modified angle (e.g., a modified azimuth angle) for the firstspeaker based on the azimuth angle mapping function.

The azimuth angle mapping function comprises:

$\phi^{\prime} = \left\{ \begin{matrix}{{\frac{\phi_{right}^{repro} + {180{^\circ}}}{\phi_{right}^{nominal} + {180{^\circ}}} \cdot \left( {\phi + {180{^\circ}}} \right)} - {180{^\circ}}} & {{{for}\mspace{14mu} - {180{^\circ}}} \leq \phi < \phi_{right}^{nominal}} \\{{\frac{\phi_{left}^{repro} - \phi_{right}^{repro}}{\phi_{left}^{nominal} - \phi_{right}^{nominal}} \cdot \left( {\phi - \phi_{right}^{nominal}} \right)} + \phi_{right}^{repro}} & {{{for}\mspace{14mu} \phi_{right}^{nominal}} \leq \phi < \phi_{left}^{nominal}} \\{{\frac{{180{^\circ}} - \phi_{left}^{repro}}{{180{^\circ}} - \phi_{left}^{nominal}} \cdot \left( {\phi - \phi_{left}^{nominal}} \right)} + \phi_{left}^{repro}} & {{{for}\mspace{14mu} \phi_{left}^{nominal}} \leq \phi < 180^{{^\circ}}}\end{matrix} \right.$

-   wherein φ′ represents the modified azimuth angle for the first    speaker;-   φrepresents the azimuth angle for the first speaker;-   φ_(left) ^(nominal) represents a left azimuth angle of the reference    screen;-   φ_(right) ^(nominal) represents a right azimuth angle of the    reference screen;-   φ_(left) ^(rerpo) represents a left azimuth angle of the zoomed    viewing window; and,-   φ_(right) ^(repro) represents a right azimuth angle of the zoomed    viewing window.

Audio playback system 16 may modify the renderer by determining one ormore FOV parameters of a zoomed viewing window based on the scalingfactor and the one or more FOV parameters of the viewing window,determining an elevation angle mapping function for modifying anelevation angle of a speaker based on the one or more FOV parameters ofthe zoomed viewing window and the one or more FOV parameters of thereference screen, and modifying an elevation angle for a first speakerof the one or more speakers to generate a modified elevation angle forthe first speaker based on the elevation angle mapping function,.

The elevation angle mapping function comprises:

$\theta^{\prime} = \left\{ \begin{matrix}{{\frac{\theta_{bottom}^{repro} + {90{^\circ}}}{\theta_{bottom}^{nominal} + {90{^\circ}}} \cdot \left( {\theta + {90{^\circ}}} \right)} - {90{^\circ}}} & {{{for}\mspace{14mu} - {90{^\circ}}} \leq \theta < \theta_{bottom}^{nominal}} \\{{\frac{\theta_{top}^{repro} - \theta_{bottom}^{repro}}{\theta_{top}^{nominal} - \theta_{bottom}^{nominal}} \cdot \left( {\theta - \theta_{bottom}^{nominal}} \right)} + \theta_{bottom}^{repro}} & {{{for}\mspace{14mu} \theta_{bottom}^{nominal}} \leq \theta < \theta_{top}^{nominal}} \\{{\frac{{90{^\circ}} - \theta_{top}^{repro}}{{90{^\circ}} - \theta_{top}^{nominal}} \cdot \left( {\theta - \theta_{top}^{nominal}} \right)} + \theta_{top}^{repro}} & {{{for}\mspace{14mu} \theta_{top}^{nominal}} \leq \theta < 90^{{^\circ}}}\end{matrix} \right.$

-   wherein θ′ represents the modified elevation angle for the first    speaker;-   θ represents the elevation angle for the first speaker;-   θ_(top) ^(nominal) represents a top elevation angle of the reference    screen;-   θ_(bottom) ^(nominal) represents a bottom elevation angle of the    reference screen;-   θ_(top) ^(repro) represents a top elevation angle of the zoomed    viewing window; and,-   θ_(bottom) ^(repro) represents a bottom elevation angle of the    zoomed viewing window.

Audio playback system 16 may determine the one or more FOV parameters ofthe zoomed viewing window by determining one or more azimuth angles forthe zoomed viewing window based on one or more azimuth angles for theviewing window and the scaling factor. Audio playback system 16 maydetermine the one or more FOV parameters of the zoomed viewing window bydetermining one or more elevation angles for the zoomed viewing windowbased on one or more elevation angles for the viewing window and thescaling factor. Audio playback system 16 may determine the center of thereference screen based on the one or more FOV parameters of thereference screen and determine the center of the viewing window based onthe one or more FOV parameters of the viewing window.

Audio playback system 16 may be configured to determine a renderer forthe encoded audio data, modify the renderer based on the center of theviewing window and the center of the reference screen, and render theHOA audio signal over the one or more speakers based on the modifiedrenderer and the encoded audio data.

Audio playback system 16 may determine the center of the viewing windowaccording to the following algorithm:

-   originalWidth=originalAngles.azi(1)-originalAngles.azi(2);-   originalHeight=originalAngles.ele(1)-originalAngles.ele(2);-   newWidth=newAngles.azi(1)-newAngles.azi(2)-   newHeight=newAngles.ele(1)-newAngles.ele(2);-   originalCenter.azi=originalAngles.azi(1)-originalWidth*0.5;-   originalCenter.ele=originalAngles.ele(1)-originalHeight*0.5;-   newCenter.azi=newAngles.azi(1)-newWidth*0.5;-   newCenter.ele=newAngles.ele(1)-newHeight*0.5,-   wherein “originalWidth” represents a width of the reference screen;    “originalHeight”-   represents a height of the reference screen; “originalAngles.azi(1)”    represents a first-   azimuth angle of the reference screen: “originalAngles.azi(2)”    represents a second-   azimuth angle of the reference screen; “originalAngles.ele(1)”    represents a first-   elevation angle of the reference screen; “originalAngles.ele(2)”    represents a second-   elevation angle of the reference screen; “newWidth” represents a    width of the viewing-   window; “newHeight” represents a height of the viewing window;    “newAngles.azi(1)”-   represents a first azimuth angle of the viewing window;    “newAngles.azi(2)” represents-   a second azimuth angle of the viewing window; “newAngles.ele(1)”    represents a first-   elevation angle of the viewing window; “newAngles.ele(2)” represents    a second-   elevation angle of the viewing window; “originalCenter.azi”    represents the azimuth-   angle of the center of the reference screen; “originalCenter.ele”    represents the elevation-   angle of the center of the reference screen; “neweenter.azi”    represents the azimuth-   angle of the center of the viewing window; “newCenter.ele”    represents the elevation-   angle of the center of the viewing window.

Audio playback system 16 may rotate the sound field from the center ofthe reference screen to the center of the viewing window.

The HOA audio signal may be part of an MPEG-H 3D compliant bitstream.The viewing window may, for example, be a reproduction screen or aportion of a reproduction screen. The viewing window may also correspondto a local screen. The reference screen may, for example, be aproduction screen.

Audio playback system 16 may be configured to receive a syntax elementindicating values for the one or more FOV parameters of the referencescreen correspond to default values and/or receive a syntax elementindicating values for the one or more FOV parameters of the referencescreen correspond to signaled values included in a bitstream comprisingthe HOA audio signal.

A matrix, including a preliminary effect matrix, effect matrix,rendering matrix, final rendering matrix, or other type of matrixdescribed in this disclosure may be processed in various ways. Forexample, a matrix may be processed (e.g., stored, added, multiplied,retrieved, etc.) as rows, columns, vectors, or in other ways. It shouldbe understood that, as used in this disclosure, the term matrix mayrefer to a data structure associated with matrix data.

FIG. 21 is a flowchart illustrating an example process 940 that a systemmay perform to implement one or more techniques of this disclosure. Itwill be appreciated that process 940 may performed by a variety ofsystems and/or devices, in accordance with the various aspects of thisdisclosure. For ease of discussion, however, process 940 is describedherein as being performed by the audio playback system and/or variouscomponents thereof. Process 940 may begin when the audio playback system16 obtains HOA coefficients of an HOA audio signal (941). For instance,the audio decoding device 24 of the audio playback system 16 may obtainHOA coefficients 11′ from the audio bitstream 21. In turn, the audioplayback system 16 may generate an effect matrix based on spatialdirections of the HOA coefficients 11′ (942). For instance, the audioplayback system 16 may generate a preliminary effect matrix {tilde over(F)} based on the spatial directions of the HOA coefficients 11′, anduse the preliminary effect matrix {tilde over (F)} to generate theeffect matrix (or “final” effect matrix) F.

The audio playback system 16 may compute a new rendering matrix usingthe effect matrix F (944). For instance, the audio playback system 16may compute the new rendering matrix (denoted by the symbol ‘D’),according to the formula D=FRY, where ‘R’ denotes an original renderingmatrix. The audio playback system 16 may use the new rendering matrix Dto render the HOA signal to loudspeaker feeds (946). For instance, theaudio playback system 16 may use the new rendering matrix D to renderthe HOA coefficients 11′ to one or more of the loudspeaker feeds 25 tobe played back via one or more of speakers 3. In turn, the audioplayback system 16 may output the loudspeaker feeds 25 to drive one ormore loudspeakers, such as one or more of speakers 3 (948).

FIG. 22 is a flowchart illustrating an example process 960 that a systemmay perform to implement one or more techniques of this disclosure. Itwill be appreciated that process 960 may performed by a variety ofsystems and/or devices, in accordance with the various aspects of thisdisclosure. For ease of discussion, however, process 960 is describedherein as being performed by the audio playback system and/or variouscomponents thereof. Process 960 may begin when the audio playback system16 obtains HOA coefficients of an HOA audio signal (961). For instance,the audio decoding device 24 of the audio playback system 16 may obtainHOA coefficients 11′ from the audio bitstream 21.

In turn, the audio playback system 16 may perform loudness compensationto generate an effect matrix (962). For instance, the audio playbacksystem 16 may perform loudness compensation to compensate for one ormore effects of mapping. The audio playback system 16 may performloudness compensation to equalize one or more undesireddirection-dependent loudness differences caused by the spatialstretching and/or squeezing of the effect matrix, as may be caused bythe mapping. The audio playback system 16 may compute a new renderingmatrix using the effect matrix (964). For instance, the audio playbacksystem 16 may compute the new rendering matrix (denoted by the symbol‘D’), according to the formula D=FRY, where ‘R’ denotes an originalrendering matrix, and ‘F’ denotes the effect matrix generated usingloudness compensation.

The audio playback system 16 may use the new rendering matrix D torender the HOA signal to loudspeaker feeds (966). For instance, theaudio playback system 16 may use the new rendering matrix D to renderthe HOA coefficients 11′ to one or more of the loudspeaker feeds 25 tobe played back via one or more of speakers 3. In turn, the audioplayback system 16 may output the loudspeaker feeds 25 to drive one ormore loudspeakers, such as one or more of speakers 3 (968).

FIG. 23 is a flowchart illustrating an example process 980 that a systemmay perform to implement one or more techniques of this disclosure. Itwill be appreciated that process 980 may performed by a variety ofsystems and/or devices, in accordance with the various aspects of thisdisclosure. For ease of discussion, however, process 980 is describedherein as being performed by the audio playback system and/or variouscomponents thereof. Process 980 may begin when the audio playback system16 obtains HOA coefficients of an HOA audio signal (981). For instance,the audio decoding device 24 of the audio playback system 16 may obtainHOA coefficients 11′ from the audio bitstream 21.

In turn, the audio playback system 16 may generate an effect matrixusing loudness compensation and using spatial directions of the HOAcoefficients 11′ (982). For instance, the audio playback system 16 maycompute or generate a preliminary effects matrix {tilde over (F)}according to one or more of the formulas described above. Additionally,the audio playback system 16 may compute a loudness value by using anHOA rendering matrix R for each spatial direction of the HOAcoefficients 11′. In turn, the audio playback system 16 may compute thefinal effect matrix using the mode matrix computed as described above.

The audio playback system 16 may compute a new rendering matrix usingthe effect matrix (984). For instance, the audio playback system 16 maycompute the new rendering matrix (denoted by the symbol ‘D’), accordingto the formula D=FRY, where ‘R’ denotes an original rendering matrix,and ‘F’ denotes the effect matrix generated using loudness compensationand the spatial directions of the HOA coefficients 11′.

The audio playback system 16 may use the new rendering matrix D torender the HOA signal to loudspeaker feeds (986). For instance, theaudio playback system 16 may use the new rendering matrix D to renderthe HOA coefficients 11′ to one or more of the loudspeaker feeds 25 tobe played back via one or more of speakers 3. In turn, the audioplayback system 16 may output the loudspeaker feeds 25 to drive one ormore loudspeakers, such as one or more of speakers 3 (988).

The foregoing techniques may be performed with respect to any number ofdifferent contexts and audio ecosystems. A number of example contextsare described below, although the techniques should be limited to theexample contexts. One example audio ecosystem may include audio content,movie studios, music studios, gaming audio studios, channel based audiocontent, coding engines, game audio stems, game audio coding/renderingengines, and delivery systems.

The movie studios, the music studios, and the gaming audio studios mayreceive audio content. In some examples, the audio content may representthe output of an acquisition. The movie studios may output channel basedaudio content (e.g., in 2.0, 5.1, and 7.1) such as by using a digitalaudio workstation (DAW). The music studios may output channel basedaudio content (e.g., in 2.0, and 5.1) such as by using a DAW. In eithercase, the coding engines may receive and encode the channel based audiocontent based one or more codecs (e.g., AAC, AC3, Dolby True HD, DolbyDigital Plus, and DTS Master Audio) for output by the delivery systems.The gaming audio studios may output one or more game audio stems, suchas by using a DAW. The game audio coding/rendering engines may code andor render the audio stems into channel based audio content for output bythe delivery systems. Another example context in which the techniquesmay be performed comprises an audio ecosystem that may include broadcastrecording audio objects, professional audio systems, consumer on-devicecapture, HOA audio format, on-device rendering, consumer audio, TV, andaccessories, and car audio systems.

The broadcast recording audio objects, the professional audio systems,and the consumer on-device capture may all code their output using HOAaudio format. In this way, the audio content may be coded using the HOAaudio format into a single representation that may be played back usingthe on-device rendering, the consumer audio, TV, and accessories, andthe car audio systems. In other words, the single representation of theaudio content may be played back at a generic audio playback system(i.e., as opposed to requiring a particular configuration such as 5.1,7.1, etc.), such as audio playback system 16.

Other examples of context in which the techniques may be performedinclude an audio ecosystem that may include acquisition elements, andplayback elements. The acquisition elements may include wired and/orwireless acquisition devices (e.g., Eigen microphones), on-devicesurround sound capture, and mobile devices (e.g., smartphones andtablets). In some examples, wired and/or wireless acquisition devicesmay be coupled to mobile device via wired and/or wireless communicationchannel(s). As used herein, the term “coupled” may include various typesof connections. For instance, memory device components of a device maybe “coupled” to one or more processors (e.g. processing circuitry) ifthe memory devices are communicatively connected, such as by way of abus.

In accordance with one or more techniques of this disclosure, the mobiledevice may be used to acquire a sound field. For instance, the mobiledevice may acquire a sound field via the wired and/or wirelessacquisition devices and/or the on-device surround sound capture (e.g., aplurality of microphones integrated into the mobile device). The mobiledevice may then code the acquired sound field into the HOA coefficientsfor playback by one or more of the playback elements. For instance, auser of the mobile device may record (acquire a sound field of) a liveevent (e.g., a meeting, a conference, a play, a concert, etc.), and codethe recording into HOA coefficients.

The mobile device may also utilize one or more of the playback elementsto playback the HOA coded sound field. For instance, the mobile devicemay decode the HOA coded sound field and output a signal to one or moreof the playback elements that causes the one or more of the playbackelements to recreate the sound field. As one example, the mobile devicemay utilize the wireless and/or wireless communication channels tooutput the signal to one or more speakers (e.g., speaker arrays, soundbars, etc.). As another example, the mobile device may utilize dockingsolutions to output the signal to one or more docking stations and/orone or more docked speakers (e.g., sound systems in smart cars and/orhomes). As another example, the mobile device may utilize headphonerendering to output the signal to a set of headphones, e.g., to createrealistic binaural sound.

In some examples, a particular mobile device may both acquire a 3D soundfield and playback the same 3D sound field at a later time. In someexamples, the mobile device may acquire a 3D sound field, encode the 3Dsound field into HOA, and transmit the encoded 3D sound field to one ormore other devices (e.g., other mobile devices and/or other non-mobiledevices) for playback.

Yet another context in which the techniques may be performed includes anaudio ecosystem that may include audio content, game studios, codedaudio content, rendering engines, and delivery systems. In someexamples, the game studios may include one or more DAWs which maysupport editing of HOA signals. For instance, the one or more DAWs mayinclude HOA plugins and/or tools which may be configured to operate with(e.g., work with) one or more game audio systems. In some examples, thegame studios may output new stem formats that support HOA. In any case,the game studios may output coded audio content to the rendering engineswhich may render a sound field for playback by the delivery systems.

The techniques may also be performed with respect to exemplary audioacquisition devices. For example, the techniques may be performed withrespect to an Eigen microphone which may include a plurality ofmicrophones that are collectively configured to record a 3D sound field.In some examples, the plurality of microphones of Eigen microphone maybe located on the surface of a substantially spherical ball with aradius of approximately 4cm. In some examples, the audio encoding device20 may be integrated into the Eigen microphone so as to output audiobitstream 21 directly from the microphone.

Another exemplary audio acquisition context may include a productiontruck which may be configured to receive a signal from one or moremicrophones, such as one or more Eigen microphones. The production truckmay also include an audio encoder, such as audio encoding device 20 ofFIG. 3.

The mobile device may also, in some instances, include a plurality ofmicrophones that are collectively configured to record a 3D sound field.In other words, the plurality of microphone may have X, Y, Z diversity.In some examples, the mobile device may include a microphone which maybe rotated to provide X, Y, Z diversity with respect to one or moreother microphones of the mobile device. The mobile device may alsoinclude an audio encoder, such as audio encoding device 20 of FIG. 3.

A ruggedized video capture device may further be configured to record a3D sound field. In some examples, the ruggedized video capture devicemay be attached to a helmet of a user engaged in an activity. Forinstance, the ruggedized video capture device may be attached to ahelmet of a user whitewater rafting. In this way, the ruggedized videocapture device may capture a 3D sound field that represents the actionall around the user (e.g., water crashing behind the user, anotherrafter speaking in front of the user, etc.).

The techniques may also be performed with respect to an accessoryenhanced mobile device, which may be configured to record a 3D soundfield. In some examples, the mobile device may be similar to the mobiledevices discussed above, with the addition of one or more accessories.For instance, an Eigen microphone may be attached to the above notedmobile device to form an accessory enhanced mobile device. In this way,the accessory enhanced mobile device may capture a higher qualityversion of the 3D sound field than just using sound capture componentsintegral to the accessory enhanced mobile device.

Example audio playback devices that may perform various aspects of thetechniques described in this disclosure are further discussed below. Inaccordance with one or more techniques of this disclosure, speakersand/or sound bars may be arranged in any arbitrary configuration whilestill playing back a 3D sound field. Moreover, in some examples,headphone playback devices may be coupled to audio decoding device 24via either a wired or a wireless connection. In accordance with one ormore techniques of this disclosure, a single generic representation of asound field may be utilized to render the sound field on any combinationof the speakers, the sound bars, and the headphone playback devices.

A number of different example audio playback environments may also besuitable for performing various aspects of the techniques described inthis disclosure. For instance, a 5.1 speaker playback environment, a 2.0(e.g., stereo) speaker playback environment, a 9.1 speaker playbackenvironment with full height front loudspeakers, a 22.2 speaker playbackenvironment, a 16.0 speaker playback environment, an automotive speakerplayback environment, and a mobile device with ear bud playbackenvironment may be suitable environments for performing various aspectsof the techniques described in this disclosure.

In accordance with one or more techniques of this disclosure, a singlegeneric representation of a sound field may be utilized to render thesound field on any of the foregoing playback environments. Additionally,the techniques of this disclosure enable a renderer to render a soundfield from a generic representation for playback on the playbackenvironments other than that described above. For instance, if designconsiderations prohibit proper placement of speakers according to a 7.1speaker playback environment (e.g., if it is not possible to place aright surround speaker), the techniques of this disclosure enable arender to compensate with the other 6 speakers such that playback may beachieved on a 6.1 speaker playback environment.

Moreover, a user may watch a sports game while wearing headphones. Inaccordance with one or more techniques of this disclosure, the 3D soundfield of the sports game may be acquired (e.g., one or more Eigenmicrophones may be placed in and/or around the baseball stadium), HOAcoefficients corresponding to the 3D sound field may be obtained andtransmitted to a decoder, the decoder may reconstruct the 3D sound fieldbased on the HOA coefficients and output the reconstructed 3D soundfield to a renderer, the renderer may obtain an indication as to thetype of playback environment (e.g., headphones), and render thereconstructed 3D sound field into signals that cause the headphones tooutput a representation of the 3D sound field of the sports game.

In each of the various instances described above, it should beunderstood that the audio encoding device 20 may perform a method orotherwise comprise means to perform each step of the method for whichthe audio encoding device 20 is configured to perform. In someinstances, the means may comprise one or more processors. In someinstances, the one or more processors may represent a special purposeprocessor configured by way of instructions stored to a non-transitorycomputer-readable storage medium. In other words, various aspects of thetechniques in each of the sets of encoding examples may provide for anon-transitory computer-readable storage medium having stored thereoninstructions that, when executed, cause the one or more processors toperform the method for which the audio encoding device 20 has beenconfigured to perform.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media. Data storage media may be any availablemedia that can be accessed by one or more computers or one or moreprocessors to retrieve instructions, code and/or data structures forimplementation of the techniques described in this disclosure. Acomputer program product may include a computer-readable medium.

Likewise, in each of the various instances described above, it should beunderstood that the audio decoding device 24 may perform a method orotherwise comprise means to perform each step of the method for whichthe audio decoding device 24 is configured to perform. In someinstances, the means may comprise one or more processors. In someinstances, the one or more processors may represent a special purposeprocessor configured by way of instructions stored to a non-transitorycomputer-readable storage medium. In other words, various aspects of thetechniques in each of the sets of encoding examples may provide for anon-transitory computer-readable storage medium having stored thereoninstructions that, when executed, cause the one or more processors toperform the method for which the audio decoding device 24 has beenconfigured to perform.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), processing circuitry (such asprogrammable processing circuitry, fixed function circuitry, or acombination of programmable processing circuitry and fixed functioncircuitry), general purpose microprocessors, application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Accordingly,the term “processor,” as used herein may refer to any of the foregoingstructure or any other structure suitable for implementation of thetechniques described herein. In addition, in some aspects, thefunctionality described herein may be provided within dedicated hardwareand/or software modules configured for encoding and decoding, orincorporated in a combined codec. Also, the techniques could be fullyimplemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various aspects of the techniques have been described. These and otheraspects of the techniques are within the scope of the following claims.

What is claimed is:
 1. A device for rendering a higher order ambition(HOA) audio signal, the device comprising: a memory configured to storethe HOA audio signal; and one or more processors, coupled to the memory,the one or more processors being configured to: perform a loudnesscompensation process as part of generating an effect matrix; and renderthe HOA audio signal based on the effect matrix.
 2. The device of claim1, wherein the one or more processors are configured to compensate forloudness for a plurality of spatial directions based on a renderingmatrix.
 3. The device of claim 1, wherein the one or more processors areconfigured to compensate for loudness for a plurality of spatialdirections based on a mapping function.
 4. The device of claim 1,wherein the one or more processors are configured to determine, based ona production screen size and a reproduction window size with respect tovideo data associated with the HOA audio signal, a minimum error betweena plurality of original sound locations associated with objects of theHOA audio signal and a plurality of corresponding mapped destinationsassociated with the objects of the HOA audio signal.
 5. The device ofclaim 1, wherein the one or more processors are configured to determine,using a production screen size and a reproduction window size withrespect to video data associated with the HOA audio signal, an energynormalization between a plurality of original sound locations associatedwith objects of the HOA audio signal and a plurality of correspondingmapped destinations associated with the objects of the HOA audio signal.6. The device of claim 1, wherein the one or more processors are furtherconfigured to: determine a renderer for encoded audio data; modify therenderer based on one or more field of view (FOV) parameters of aviewing window and the one or more FOV parameters of a reference screen;and use both of the effect matrix and the modified renderer to renderthe HOA audio signal.
 7. The device of claim 6, further comprising oneor more speakers, wherein the one or more processors are configured todetermine the renderer based on a speaker configuration associated withthe one or more speakers of the device.
 8. The device of claim 6,wherein the renderer comprises one or more of a rendering format or analgorithm for converting the encoded audio data to a reproductionformat.
 9. The device of claim 6, wherein the one or more processors arefurther configured to: based on the one or more FOV parameters of thereference screen and the one or more FOV parameters of the viewingwindow, determine an angle mapping function for modifying an angle of aspeaker; based on the angle mapping function, modify an angle for afirst speaker of one or more speakers to generate a modified angle forthe first speaker; and use the modified angle for the first speaker tomodify the renderer.
 10. The device of claim 6, further comprising adisplay configured to output one or both of the viewing window or azoomed viewing window that is based on the viewing window, wherein thedisplay is coupled to the one or more processors, wherein the one ormore processors are further configured to determine, in response to auser initiated zoom function, one or more FOV parameters of the zoomedviewing window, and wherein the one or more processors are configured tomodify the renderer based on the one or more FOV parameters of thereference screen and the one or more FOV parameters of the zoomedviewing window.
 11. The device of claim 10, wherein the one or moreprocessors are configured to: obtain a scaling factor in response to auser initiated zoom operation; based on the scaling factor and the oneor more FOV parameters of the viewing window, determine one or more FOVparameters of a zoomed viewing window; based on the one or more FOVparameters of the zoomed viewing window and the one or more FOVparameters of the reference screen, determine an angle mapping functionfor modifying an angle of a speaker; and based on the angle mappingfunction, modify an angle for a first speaker of the one or morespeakers to generate a modified angle for the first speaker.
 12. Thedevice of claim 10, further comprising a display for displaying one ormore of the viewing window or the zoomed viewing window, wherein thedisplay is coupled to the one or more processors, and wherein the one ormore processors are configured to: determine one or more azimuth anglesfor the zoomed viewing window based on a scaling factor and one or moreazimuth angles for the viewing window that is output via the display;and determine the one or more FOV parameters of the zoomed viewingwindow that is output via the display, wherein the one or moreprocessors are further configured to determine one or more elevationangles for the zoomed viewing window based on one or more elevationangles for the viewing window and the scaling factor.
 13. The device ofclaim 10, wherein the one or more FOV parameters for the referencescreen comprise at least one of one or more azimuth angles for thereference screen or one or more elevation angles for the referencescreen.
 14. The device of claim 10, wherein the one or more FOVparameters for the viewing window comprise at least one of one or moreazimuth angles for the viewing window or one or more elevation anglesfor the viewing window.
 15. The device of claim 10, wherein the one ormore processors are configured to render the HOA audio signal based on ascaling factor obtained in response to a user initiated zoom operationand on the effect matrix.
 16. The device of claim 10, wherein the one ormore FOV parameters for the reference screen comprise a location of acenter of the reference screen and a location of a center of the viewingwindow.
 17. The device of claim 16, wherein the one or more processorsare further configured to: determine the center of the reference screenbased on the one or more FOV parameters of the reference screen; anddetermine the center of the viewing window based on the one or more FOVparameters of the viewing window.
 18. The device of claim 16, furthercomprising: a display configured to output one or both of the referencescreen or the viewing window; and one or more loudspeakers, wherein theone or more processors are coupled to the one or more loudspeakers,wherein the one or more processors are coupled to the display, andwherein the one or more processors are configured to: determine arenderer for the encoded audio data; modify the renderer based on thecenter of the viewing window and the center of the reference screen; andrender, for playback via the one or more loudspeakers, the HOA audiosignal based on the effect matrix and the modified renderer.
 19. Thedevice of claim 16, wherein the one or more processors are furtherconfigured to: rotate a sound field of the HOA audio signal from thecenter of the reference screen to the center of the viewing window thatis output via the display.
 20. The device of claim 10, wherein the oneor more processors are further configured receive a syntax elementindicating whether rendering of the HOA audio signal based on the one ormore field of view (FOV) parameters of the reference screen and the oneor more FOV parameters of the viewing window is enabled.
 21. The deviceof claim 1, wherein the device further comprises at least one speakercoupled to the one or more processors, and wherein the one or moreprocessors are configured to generate a loudspeaker feed to drive the atleast one speaker.
 22. The device of claim 1, wherein the device furthercomprises a display for displaying a viewing window, wherein the one ormore processors are coupled to the display, and wherein the one or moreprocessors are configured to determine one or more field of view (FOV)parameters of a viewing window that is output via the display.
 23. Thedevice of claim 1, wherein the one or more processors are furtherconfigured to decode the HOA audio signal to determine a plurality ofHOA coefficients, and wherein the one or more processors are configuredto render the HOA coefficients as part of rendering the HOA audiosignal.
 24. The device of claim 1, wherein the one or more processorsare further configured to: generate a mode matrix for nine-hundredsampling points of a sphere; modify the mode matrix based on the one ormore FOV parameters of the reference screen and the one or more FOVparameters of the viewing window to generate an effect matrix; andrender HOA coefficients of the HOA audio signal based on the effectmatrix.
 25. The device of claim 1, further comprising a television thatincludes: the memory; the one or more processors; a communicationinterface configured to receive audio data and video data; one or morespeakers for outputting the rendered audio signal; and a displayconfigured to output at least a portion of the video data.
 26. Thedevice of claim 1, further comprising a receiver device that includesthe memory and the one or more processors, wherein the receiver deviceis communicatively coupled to one or more speakers.
 27. A method forrendering a higher order ambition (HOA) audio signal, the methodcomprising: performing a loudness compensation process as part ofgenerating an effect matrix; and rendering the HOA audio signal based onthe effect matrix.
 28. The method of claim 27, wherein performing theloudness compensation process comprises compensating for loudness for aplurality of spatial directions based on a rendering matrix.
 29. Themethod of claim 27, wherein performing the loudness compensation processcomprises compensating for loudness for a plurality of spatialdirections based on a mapping function.
 30. The method of claim 27,wherein performing the loudness compensation process comprisesdetermining, using a production screen size and a reproduction windowsize with respect to video data associated with the HOA audio signal, aminimum error between a plurality of original sound locations associatedwith objects of the HOA audio signal and a plurality of correspondingmapped destinations associated with the objects of the HOA audio signal.31. The method of claim 27, wherein performing the loudness compensationprocess comprises determining, using a production screen size and areproduction window size with respect to video data associated with theHOA audio signal, an energy normalization between a plurality oforiginal sound locations associated with objects of the HOA audio signaland a plurality of corresponding mapped destinations associated with theobjects of the HOA audio signal.
 32. An apparatus for rendering a higherorder ambition (HOA) audio signal, the apparatus comprising: means forperforming a loudness compensation process as part of generating aneffect matrix; and means for rendering the HOA audio signal based on theeffect matrix.
 33. A device for rendering a higher order ambition (HOA)audio signal, the device comprising: a memory configured to store audiodata associated with the HOA audio signal; and one or more processorscoupled to the memory, the one or more processors being configured to:detect a zooming event with respect to video data associated with theHOA audio signal; in response to the detection of the zooming event,generate a mode matrix based on an order of the HOA signal; and renderthe HOA audio signal based on the mode matrix.
 34. The device of claim33, wherein the one or more processors are further configured to:locally generate a preliminary effect matrix based on the mode matrixand spatial directions of HOA coefficients of the HOA audio signal; andrender the HOA signal based on the locally generated preliminary effectmatrix.
 35. The device of claim 34, wherein the one or more processorsare further configured to: generate a rendering matrix using thepreliminary effect matrix; and render the HOA signal based on therendering matrix.
 36. The device of claim 33, further comprising atelevision that includes: the memory; the one or more processors; one ormore speakers for outputting the rendered audio signal; and a displayconfigured to output video data.
 37. The device of claim 33, wherein togenerate the mode matrix based on the order of the HOA signal, the oneor more processors are configured to apply the formula M=(N+2)², whereinN denotes the order of the HOA signal, and wherein M denotes a number ofsampling points used in generating the mode matrix.
 38. The device ofclaim 33, further comprising a receiver device that includes the memoryand the one or more processors, wherein the receiver device iscommunicatively coupled to one or more speakers.